Development Document for Effluent Limitations Guidelines
and New Source Performance Standards for the
COPPER, NICKEL,
CHROMIUM, AND ZINC
Segment of the Electroplating
Point Source Category
MARCH 1974
U.S. ENVIRONMENTAL PROTECTION AGENCY
« Washington, D.C 20460
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DEVELOPMENT DOCUMENT
for
EFFLUENT LIMITATIONS GUIDELINES
and
NEW SOURCE PERFORMANCE STANDARDS
for the
COPPER, NICKEL, CHROMIUM, AND ZINC
SEGMENT OF THE ELECTROPLATING
POINT SOURCE CATEGORY
Russell Ei Train
Administrator
Roger Strelow
Acting Assistant Administrator for Air & Water Programs
Allen Cywin
Director, Effluent Guidelines Division
Kit R. Krickenberger
Project Officer
March 1974
Effluent Guidelines Division
Office of Air and Water Programs
U.S. Environmental Protection Agency
Washington, D.C. 20460
For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402 • Price $2.40
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ABSTRACT
This document presents the findings of an extensive study of the
electroplating industry by the Environmental Protection Agency
for the purpose of developing effluent limitations guidelines,
standards of performance, and pretreatment standards for the
industry to implement Sections 304(b) and 306 of the "Act."
Effluent limitations guidelines for the copper, nickel, chromium,
and zinc segment contained herein set forth the degree of
effluent reduction attainable through the application of the best
practicable control technology currently available and the degree
of effluent reduction attainable through the application of the
best available technology economically achievable which must be
achieved by existing point sources by July 1, 1977 and July 1,
1983, respectively. The standards of performance for new souces
contained herein set forth the degree of effluent reduction which
is achievable through the ^application of the best available
demonstrated control technology, processes, operating methods, or
other alternatives. The proposed regulations for all three
levels of technology set forth above are presented in Section II,
R ECOMMENDATIONS.
Supportive data and rationale for development of the proposed
effluent limitations guidelines and standards of performance are
contained in this report.
Preceding page blank
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CONTENTS
Section
I CONCLUSIONS 1
IT RECOMMENDATIONS 3
Best Practicable Control Technology 3
Currently Available
Best Available Technology Economically 3
Achievable
New Source Performance Standards 3
III INTRODUCTION 7
Purpose and Authority 7
Summary of Methods Used for Development 8
of the Effluent Limitations Guidelines
and Standards of Performance
Information Sources 9
General Description of the 9
Electroplating Industry
13
IV INDUSTRY CATEGORIZATION 13
Introduction 13
Objectives of Categorization
The Relationship of Electroplating 13
and Metal Finishing
Profile of Production Processes 13
Materials Receiving Electroplates 19
Factors Considered in Categorization 20
V WASTE CHARACTERIZATION 29
Introduction 29
Specific Water Uses 32
Quantity of Wastes 33
Sources of Waste
VI SELECTION OF POLLUTANT PARAMETERS 49
Introduct ion 4 9
Metal Finishing Wastewater Constituents 49
Electroplating Wastewater Constituents 49
Wastewater Constituents and Parameters 52
of Pollutional Significance
Rationale for the selection of 52
Wastewater constituents and Parameters
Rationale for the Selection of Total 54
Metal as A Pollutant Parameter
Rationale for Rejection of Other 57
Wastewater Constituents as Pollutants
¥11 CONTROL AND TREATMENT TECHNOLOGY 61
Introduction 61
Chemical Treatment Technology 61
Preceding page blank
v
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Unit Operations 66
Practical operating Systems 73
Precipitation of Metal Sulfides 75
Water Conservation Through Control 77
Technology
Methods of Achieving No Discharge 168
of Pollutants
VIII COST, ENERGY, AND NONWATER QUALITY 113
ASPECTS
Introduction 113
Treatment and Control Costs 113
Cost Effectiveness and Treating 118
Procedures
Nonwater Quality Aspects 119
IX BEST PRACTICABLE CONTROL TECHNOLOGY 123
CURRENTLY AVAILABLE, GUIDELINES,
AND LIMITATIONS
Introduction ^3
Industry Category and Subcategory
Covered
Identification of Best Practicable 124
Control Technology Currently Available
Rationale for Selecting the Best 126
Practicable Control Technology
Currently Available
Waste Management Techniques Considered 126
Normal practice in the Electro-
plating Industry
Degree of Pollution Reduction Based 127
on Existing Performance by Plants
of Various, Sizes, Ages, and
Processes Using Various Control
and Treatment Technology
Determination of Effluent Limitations 163
Selection of Best Practicable
Additional Factors Considered in 167
Selection of Best Practicable
Control Technology Currently
Available
Guidelines for the Application 171
of Effluent Limitations
X BEST AVAILABLE TECHNOLOGY ECONOMICALLY 187
ACHIEVABLE, GUIDELINES AND LIMITATIONS
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Introduction 187
Industry Category and Subcategory 188
Covered
Identification of Best Available 188
Technology Economically Achievable
Rationale for Selection of Best 188
Available Technology Economically
Achievable
Effluent Limitations Based on the 190
Application of Best Available
Technology Economically Achievable
Guidelines for the Application of 191
Effluent Limitations
XI NEW SOURCE PERFORMANCE STANDARDS 193
Introduction 193
Industry Category and Subcategory 194
Covered
Identification of Control and 194
Treatment Technology Applicable to
Performance Standards and Pre-
treatment Standards for New Sources
Rationale for Selection of Control 194
and Treatment Technology Applicable
to New source performance standards
Standards of Performance 195
Applicable to New Sources
Guidelines for the Applications of 196
New Sources Performance standards
197
XII ACKNOWLEDGEMENTS
199
XIII REFERENCES
203
XIV GLOSSARY
via.
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TABLES
numbers 1§3§
1 Recommended Effluent Limitations for 4
the Electroplating Industry to be
Achieved by July 1, 1977, based on
Best Practicable Control Technology
Currently Available (BPCTCA)
2 Recommended Standards of Performance 5
for the Electroplating Industry to
be Achieved by New Sources
3 Process for Plating on Steel 15
4 Processes for Plating on Zinc Die Castings 16
5 processes for Plating on Brass 17
6 processes for Plating on Aluminum I8
7 processes for Plating on Plastics 18
8 Distribution of Electroplate According 2°
to Type of Basis Material
9 processing Sequences Decorative copper 22
Chromium Plating
19 processing Sequences for Nickel Plating 23
11 Processing Sequences for Chromium Plating 23
12 processing Sequences for Zinc Plating 24
13 Estimated Daily Raw Waste Load of 34
Principal Salts Used in Copper,
Nickel, Chromium, Zinc Plating and
Related Processes
14 Principal Wastewater Constituents in 35
wastes From Processes for Plating on
Steel
15 Principal Wastewater Constituents in 36
waste From Processes for Plating
on Zinc Die Castings
16 principal Wastewater constituents in 37
waste From Processes for Plating on
Brass
17 Principal Wastewater Constituents in 38
Vlll
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Waste Fran Processes for Plating
on Aluminum
18 Principal Wastewater Constituents 39
in Waste From Processes for Plating
on Plastics
19 Approximate Concentrations of Waste 51
Water constituents Prior to Treatment
From a Typical Facility Electroplating
Copper, Nickel, Chromium, and Zinc
(Plant 33-1)
20 Concentrations of Heavy Metals and 74
Cyanide Achievable by Chemical Treating
of waste Created by copper. Nickel,
Chromium and Zinc Plating and zinc
Chromating operations
21 Decomposition Products of Cyanide in 78
Rinse water From a Cyanide zinc
Electroplating Operation After
Treatment with "Kastone" Peroxygen
Compound
22 Estimated Costs for Small Electroplating 116
Facilities With No Waste Treatment
to Meet Effluent Limitations for
1977 and 1983
23 Geographical Distribution of Good 129
Electroplating Waste Treatment
Facilities Based on Initial Referrals,
Companies Contacted for Information,
and Representative Facilities Evaluated
in Detail
24 Classification by Size, Type of Facility, 132
and Effluent Discharge for 53 Electro-
plating facilities Selected for
Evaluation
25 Classification of 53 Facilities 134
Evaluated By Mix of Plating Operations
and Type of Waste Treatment and
In-Process controls
26 Source of Information and classification 135
by size and Waste Treatment Method
27 Size of Plating operations 135
28 Treated Effluent Data 139
29 Comparison of Treated Effluent Data 146
IX
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Based on Total Amperage
30 Summary of Water Use Parameters for 159
Four Plants Based on Copper, Nickel
Chromium or Zinc Plating and Ex-
cluding Nonpertinent Metal Finishing
Processes
31 Summary of Treated Effluent from 160
Copper, Nickel, Chromium or Zinc
Excluding Nonpertinent Plant
Metal Finishing Operations
32 Summary of Treated Effluent Analysis During 161
Second Round Visit for Comparison with Table 2
33 Compliance of Exemplary Plants with 165
Tentative Effluent Limitations Guidelines
34 Monthly Average Effluent Concentration 166
for Plant 33-1 Showing Improved
Results Obtained Over a 14-Month
Period
35 Comparison of Effluent Limitations for 153
BPCTCA (Table 1) in Terms of
Concentration for Various Effluent
With the Prior Interim Guideline
Concentrations
36 Typical Current Efficiencies Assumed 175
forCalculationof Plated Area
Using Equation (2)
37 English/Metric Unit Conversion 214
x
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FIGURES
Number
1. Relationship of Total Metal in Treated Water 26
Discharge to the Production Capacity of Typical
Electroplating expressed as Metal Deposited
Per Hour
2. Schematic Flow Chart for Water Flow in Chromium 30
Plating Zinc Die Castings Decorative
3. Alternative Methods of Rinsing after 31
a Processing Operation
4. Diagram of a Typical Continuous-Treatment 63
Plant
5. Integrated Treatment System 65
6. Batch Treatment of Cyanide Rinse Waters 79
by the Kastone Process
7. Schematic Presentation of Ion-Exchange 87
Application for Plating-Effluent
Treatment (7,25)
8. Schematic Presentation of Ion-Exchange 89
Operation at Plant 11-8
9. Representative Closed-Loop System for 92
Recovery of Chemicals and Water with
a Single-Effect Evaporator
10. Representative Open-Loop Evaporative 94
Recovery System
11, Closed-Loop System for Metal Finishing 95
Process Water at Rock Island Arsenal
12. Schematic Diagram of the Reverse-Osmosis 97
Process for Treating Plating Effluents
13. Schematic Diagram of Freezing Process 101
for Recovery of Water and chemicals
from Plating Rinses (37,38)
14. Schematic Diagram of Ion-Flotation 105
Cell for Treatment of Plating Effluent
15. Flow Chart for Treatment of Waste Water 110
from Cleaner and Acid Dip When Plating
Operations Have Separate Stream Treatment
16. Effective of Size of Plating Plant on Investment 114
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Cost of Waste-Treatment Facility
17. Cost Effectiveness of Treatments and 120
In-Process Water Conservation Techniques
18. Employees Per Shift in Plating Versus 140
Cumulative Percentage of 53 Plants
19. Total Installed current for Plating 141
Versus Cumulative Percentage of
53 Plants
20. Installed Rectifier Capacity in Amperes 142
for Electroplating Versus Number of
Employees Per Shift in Electroplating
for 53 Plant Sample (Ration of Amperes
Used To Amperes Installed is Typically
65 Percent)
21. Effluent Discharge Rate Versus 143
Cumulative Percentage of 53 Plants
22. Composite of Pollutant Parameters in 145
Treated Effluent Versus Cumulative
Percentage of Plants
23. Water Use Based on Total Installed 147
Current Versus Cumulative Percentage
of 53 Plants
24. comparison of the Water Use for Plants 149
that use In-Process Chemical Recovery
Systems on One or More Plating
Operations with the Water Use of Plants
that do not Use In-Process Recovery
25. Copper In Treated Effluent ' 150
From Electroplating
26. Nickel In Treated Effluent From 151
Electroplating
27. Hexavalent Chromium In Treated 152
Effluent From Electroplating
28. Total Chromium In Treated Effluent 153
From Electroplating
29. Zinc In Treated Effluent From 154
Electroplating
30. Cyanide In Treated Effluent From 155
Electroplating
31. Suspended Solids In Treated 155
xii
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Effluent From Electroplating
32. Typical Variation in Concentration 162
of Pollutant Parameters From Analysis
of Daily composite Over a H-Month
Period Reported by Plant 11-8
33. Process Line for Example 1 179
34, Process Line for Example 2 181
35. Process line for Example 4 186
xiii
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SECTION I
CONCLUSIONS
The electroplating of copper, nickel, chromium and zinc, on
ferrous, nonferrous, and plastic materials is a single
subcategory of the electroplating point source category for the
purpose of establishing effluent limitations guidelines and
standards of performance. The consideration of other factors
such as the age of the plant, processes employed, geographical
location, wastes generated and wastewater treatment and control
techniques employed support this conclusion. The similarities of
the wastes produced by electroplating operations and the control
and treatment techniques available to reduce the discharge of
pollutants further substantiate the treatment of copper, nickel,
chromium and zinc electroplating as a single subcategory.
However, guidelines for the application of the effluent
limitations and standards of performance to specific facilities
take into account the size of the electroplating facility and the
mix of different electroplating processes possible in a single
plant.
Presently, 13 of the 53 operating plants for which sufficient
industry data were available achieve the concentrations of
pollutants and water use estimate upon which the guidelines are
based in the treated effluent using conventional chemical
treatment systems. Of these 13 plants, 11 are captive and 2 are
job shops. Verification testing on four of the plants show that
two are meeting the guidelines. One is a captive and one is a
job shop.
Only a small percentage of the raw waste generated by the
electroplating industry is discharged directly to navigable
waters without any treatment. The remainder of the industry can
achieve the requirements as set forth herein with a minimum
investment cost of $50,000 and a minimum operating cost of
$13,000/year. For larger plants plating over 100 sq m/hr (1076
sq ft/hr) the operating cost will be less than 5 percent of the
plating cost. The capital investment will be approximately
$150,000 per 100 sq m/hr ($140,000 per 1000 sq ft/hr) of plated
area. It is further estimated that no discharge of pollutants,
when required, could be achieved with increased costs of about 10
percent of the total plating costs (including land and building).
Capital investment will be approximately $100,000 to $200,000 per
100 sq m/hr (93,000 to $186,000 per 1000 sq ft/hr).
The development of data and recommendations in this document for
effluent limitations guidelines and standards of performance for
the electroplating industry (Phase I) relate to rack and barrel
electroplating of copper, nickel, chromium, and zinc. This
segment contributes about two-thirds of the total amount of
chemicals added to wastewater in the electroplating industry.
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SECTION II
Best Pr a ct icable control Technology
Cur r ep t ly ftv a il ab 1 e ~ ~~
Recommended effluent limitations for the electroplating industry
applicable to existing sources discharging to navigable waters
are summarized in Table 1. The effluent limitations guidelines
are based on the reduction of waste water pollutants and
judicious water use. The reduction of waste water pollutants is
achieved by chemical treatment of waste waters to destroy
oxidizable cyanide, reduce chromium, and remove the metals to
very low levels. Water consumption can be minimized by in-
process control technology designed to recover and reuse process
chemicals and water. The specific effluent limitations
guidelines and rationale are discussed in greater detail in
Section IX of this report.
Best .......... Avail abj-e TecfanplQgyt=EconomigaJtly=
For the electroplating industry, no discharge of process waste
water pollutants to navigable waters is recommended as the
effluent limitation to be achieved by existing point sources by
July 1, 1983. This represents the degree of effluent reduction
believed to be attainable by existing point sources through the
application of the Best Available Technology Economically
Achievable, section X of this report details the rationale of
the effluent limitations guidelines for 1983.
New source^ performance Standards
Table 2 summarizes the recommended standards of performance for
discharge to navigable waters applicable to new sources in the
electroplating industry. In the case of electroplating, a new
source is defined as an installation on which construction begins
after publication of promulgated regulations prescribing a
standard of performance.
The effluent limitations guidelines are based on the reduction of
waste water pollutants and jucicious water use. The reduction of
waste water pollutants is achieved by chemical treatment of waste
waters to destroy oxidizable cyanide, reduce chromium, and remove
to very low levels the metals. Water consumption can be
minimized by in-process control technology designed to recover
and reuse process chemicals and water. Section XI details the
reationale for the effluent limitations guidelines for new
sources .
Preceding page blank
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TABLE 1. RECOMMENDED EFFLUENT LIMITATIONS FOR THE ELECTRO-
PLATING INDUSTRY TO BE ACHIEVED BY JULY 1, 1977,
BASED ON BEST PRACTICABLE CONTROL TECHNOLOGY
CURRENTLY AVAILABLE (BPCTCA)
Parameter
Copper (Cu) (d)
Nickel (N1) (d)
Chromium
hexavalent
(Cr6+) (d)
Chromium, total
(Cri) (d) (e)
Zinc (Zn) (d)
Cyanide, oxi-
dizable (CN)
Cyanide, total
(CN) (g)
Total Suspended
Solids (TSST
pH range 6 to
9.5 (i)
Single Day
rng/sq m/op
160
160
16
160
160
(f) 16
160
h)
4800
Effluent Limi
Maximum vb)
lb/106 so ft/op
32.7
32.7
3.3
32.7
32.7
3.3
32.7
982
tations (a
)
30-Day Average ic;
mg/sq m/op
80
80
8
80
80
8
80
3200
lfa/106 sq ft
16.4
16.4
1.6
16.4
16.4
1.6
16.4
654
See Footnotes on page 6
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TABLE 2 . RECOMMENDED STANDARDS OF PERFORMANCE FOR THE
ELECTROPLATING INDUSTRY TO BE ACHIEVED BY
NEW SOURCES
Parameter
Copper (Cu) (d)
Nickel (N1) (d)
Chromium,
hexavalent
(Cr6+) (d)(e)
Chromium, total
(CrT) (d) (e)
Zinc (Zn)(d)
Cyanide, oxi- .
dizable (CN) I
Cyanide, total
(CN) (g)
Total Suspended
Solids (TSS) (
pH range 6 to
9.5 (1)
Sing!
mg/sq m/op
80
80
8
80
80
f ) 8
80
h) 2400
Standards
e Day Maxi
lb/106 sq
16.
16.
1 .
16.
16.
1.
16.
491
of Performance
mumlb) 30-Day
ft/op mg/sq m/op
4 40
4 40
6 40
4 40
4 40
6 4
4 40
1600
(a)
Average (c)
lb/106 sq ft/op
8.2
8.2
0.8
8.2
8.2
0.8
8.2
327
See Footnotes on page 6
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FOOTNOTES FOR TABLES 1 and 2
(a) The effluent limitations and standards of performance
are defined as the weight of pollutant in milligrams
discharged per square meter per operation. An operation
is defined as any step in the plating process in which
copper, chromium, or zinc metal or chromate is deposited
on a base material followed by a rinse,
(b) Single Day Maximum is the maximum value for any one day
(c) 30-Day Average is the maximum average of daily values
for any consecutive 30 days
(d) Total metal (soluble and insoluble) in sample,
(e) Total chromium (Cry) is the sum of all ionic forms
(Cr« + Cr+6).
(f) Oxidizable cyanide is defined as detectable cyanide
amenable to oxidation by chlorine according to stanard
analytical procedures,
(g) Total cyanide is defined as all detectable cyanide in
the sample following distillation according to standard
analytical procedures.
(h) Total suspended solids retained by a 0.45 micron filter
according to standard analytical procedures,
(i) A pH in the range of 8 to 9 is the best range for mini-
mizing the soluble metal-concentation during coprecipi-
tation, as discussed in Section VII.
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SECTION III
INTRODUCTION
Purpo se an d Au-bho r ity
Section 301 (b) of the Act requires the achievement by not later
than July 1, 1977, of effluent limitations for point sources,
other than publicly-owned treatment works, which are based on the
application of the best practicable control technology currently
available as defined by the Administrator pursuant to Section
301(b) of the Act. Section 301 (b) also requires the achievement
by not later than July 1, 1983, of effluent limitations for point
sources, other than publicly-owned treatment works, which are
based on the application of the best available technology
economically achievable which will result in reasonable further
progress toward the national goal of eliminating the discharge of
all pollutants, as determined in accordance with regulations
issued by the Administrator pursuant to section 30 4 {b) to the
Act. Section 306 of the Act requires the achievement by new
sources of a Federal standard of performance providing for the
control of the discharge of pollutants which reflects the great-
est degree of effluent reduction which the Administrator
determines to be achievable through the application of the best
available demonstrated control technology, processes, operating
methods, or other alternatives, including where practicable, a
standard permitting no discharge of pollutants.
Section 304 (b) of the Act requires the Administrator to publish
within one year of enactment of the Act, regulations providing
guidelines for effluent limitations setting forth the degree of
effluent reduction attainable through the application of the best
practicable control technology currently available and the degree
of effluent reduction attainable through the application of the
best control measures and practices achievable including
treatment techniques, process and procedure innovations,
operation methods and other alternatives. The regulations
proposed herein set forth effluent limitations guidelines
pursuant to Section 304 (b) of the Act for the electroplating
point source category.
Section 306 of the Act requires the Administrator, within one
year after a category of sources is included in a list published
pursuant to Section 306 (b) (1) (A) of the Act, to propose
regulations establishing Federal standards of performances for
new sources within such categories. The Administrator published
in the Federal Register of January 16, 1973 (38 FR 1624), a list
of 27 source categories.
Publication of the list constituted announcement of the
Administrator's intention of establishing, under section 306,
standards of performance applicable to new sources within the
electroplating subcategory of the metal finishing industry which
was included within the list published January 16, 1973.
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Summary ..ofMethods ^Used ifor_pevelo|3ment:=g£=-|hg=Sf|lagnt.
Limitation Guide|ines^^and^StarLda.rds^of_Performance
The effluent limitations guidelines and standards of performance
recommended herein were developed in the following manner. The
point source subcategory of electroplating was first examined to
determine whether separate limitations and standards would be
appropriate for different segments. Such subcategorization was
based upon raw material used, product design, type of basis
material, size and age of facility, number of employees,
geographic location, quantity of work processed, waste
characteristics, treatability of wastes, and rack plating versus
barrel plating. The raw-waste characteristics for each
subcategory were then identified. This included an analyses of
(1) the source and volume of water used in a process and the
sources of waste and waste waters in representative plants; and
(2) the constituents of all waste waters including those which
are potentially harmful and result in taste, odor, and color in
water or aquatic organisms. The constitutents of waste waters
which should be subject to effluent limitations guidelines and
standards of performance were then identified.
The full range of control and treatment technologies along with
their problems, limitations, and reliability, cost and energy
requirements were identified. This included in-plant and end-of-
process technologies, which are existent or capable of being
designed for each subcategory. The quantity and the chemical,
physical, and biological characteristics of each pollutant were
identified along with the reduction associated with the
application of each of the treatment and control technologies.
The environmental impacts on non-water quality aspects such as
air, solid waste, and noise were also investigated.
The information, was then evaluated to determine what levels of
technology constituted the "best practicable control technology
currently available," "best available technology economically
achievable" and the "best available demonstrated control
technology, processes, operating methods, or other alternatives,"
In identifying such technologies, various factors were
considered. These included the total cost of application of the
technology in relation to the effluent reduction benefits to be
achieved from such application, the age of equipment and
facilities involved, the process employed, the engineering
aspects of the application of various types of control techniques
process changes, nonwater quality environmental impact (including
energy requirements) and other factors.
Companies plating copper, nickel, chromium and zinc and reporting
low levels of pollutants in their waste discharge to EPA regional
offices or state authorities were contacted by telephone or
letter to develop quantitative data on volume of production (or
direct current use), water flow rate and composition of waste
water discharge. This list of companies was supplemented by
others suggested by trade associations and several suppliers of
waste treatment equipment. From the information collected from
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more than 200 companies, data on plants having a volume of
effluent flow or discharge of pollutants that reflected inferior
treatment technology were excluded from the analysis of pollutant
reductions achievable by the application of the best practical
control technology. Data from 53 companies practicing good waste
treatment were expanded by 23 plant visits and analyzed to
identify the control and treatment technologies which became the
basis for the effluent limitations and standards of performance
recommended in Section II. This group of 53 companies included
12 independent job shops employing from 16 to 200 workers. Size
in terms of installed current capacity ranged from 6,000 to
263,000 amperes among the independent shops and 3,000 to 450,000
amperes among the captive facilities. Chemical waste treatment
was practiced by all but two companies, which used evaporators to
recycle plating rinse water; 13 companies utilized integrated
chemical treatment; 13 employed evaporators to reduce the water
flow rate from one, two or three plating processees. Four
utilized ion exchange units and two used reverse osmosis for some
plating processes. Two companies were using counterflow rinses
for reclaiming plating solution dragged into rinse water. A
total of 21 companies employed batch or continuous chemical
treatment exclusively.
information^ggurces
Sources of information utilized for developing the data in
this document included the following: *
(1) Published literature (References appear in Section XIII)
(2) Trade literature
(3) Technology Transfer Program on Upgrading Metal Finishing
Facilities to Reduce Pollution, December 12-13, 1972,
sponsored by Environmental Pollution Agency
(4) Pollution Abatement seminar, sponsored by the Metal
Finishing Suppliers Association, January 23, 1973,
Cleveland, Ohio
(5| Ten EPA regional offices and 32 state pollution
abatement offices
(6) Representatives of the American Electroplaters* Society,
(AES), the Metal Finishing Suppliers" Association (MFSA)
and the National Association of Metal Finishers (NAMF)
(7) Representatives of 130 companies with facilities for
electroplating copper, nickel, chromium, or zinc, during
telephone conferences
(8) Representatives of seven companies during office
conferences
(9) Representatives of 23 companies were visited by BCL
staff members for development of detailed data
(10) Analytical verification of effluent data for five plants
engaged in electroplating copper, nickel, zinc, and/or
chromium. These five companies included captive
facilities and job shops.
Descri.Btio:ni_gf them Electroplating Industry
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The electroplating industry, a subcategory of the metal finishing
activities included in standard industrial classification (SIC)
3t71, is defined for the purpose of this document as that segment
of industry applying metallic coatings on surfaces by
electrodeposition and includes both independent (job) platers and
captive operations associated with product fabrication and
assembly. The annual dollars-added value by electroplating
exceeds $2,000,000,000. Approximately 20,000 companies are
engaged in metal finishing, approximately 3500 of these are shops
supplying only plating service. About 25 percent of this segment
is concentrated in the middle western states of Illinois,
Michigan, and Ohio. Another 20 percent is concentrated in
eastern Pennsylvania and the Atlantic coastline states of
Connecticut, Rhose Island, New York and New Jersey. The location
of captive plating facilities follows the same general pattern.
The energy consumed annually by electroplating is estimated to be
in the range of 1 to 1.5 x 109 kilowatt hours. From 9 x 107 to 1
x 108 kg (100,000 to 120,000 tons) of metal (principally copper,
nickel, zinc, and tin) is converted annually to electroplated
coatings. These coatings provide corrosion protection, wear or
erosion resistance, antifrictional characteristics, lubricity,
electrical conductivity, heat and light reflectivity or other
special surface characteristics, which enables industry to
conserve several millions of tons of critical metals, such as:
cobalt, chromium, nickel, silver and gold. Electroplated coating
thickness usually ranges from 0.0006 to 0.004 cm (0.00025 to
0.0015 inch), but thicker coatings to 0.025 or O.Oa cm (0.010 to
0,015 in.) are sometimes required for special engineering
purposes or for salvaging worn or mismachined parts.
An electroplating process includes cleaning, electroplating,
rinsing and drying. The cleaning operation consists of two or
more steps that are required for removing grease, oil, soil, and
oxide films from the basic metal surface and insuring good
electroplate adhesion. Sequential treatments in an alkaline
solution and an acid solution with intermediate rinsing are the
minimum number customary for these purposes. In the
electroplating solution, metal ions in either acid, alkaline or
neutral solutions are reduced on cathode surfaces, which are the
work pieces being plated. The metal ions in solution are usually
replenished by the dissolution of metal from anodes in bar form
or in small pieces contained in inert wire or expanded metal
baskets, but replenishment with metal salts is sometimes
practiced, especially for chromium plating. In this case, an
inert material must be selected for the anodes. Hundreds of
different electroplating solutions have been adopted
commerically, but only two or three types are utilized widely for
a single metal or alloy. Cyanide solutions are popular for
copper, zinc, and cadmium, for example, yet non-cyanide alkaline
solutions containing pyrophosphate or another chelating agent
have been adopted recently for zinc and copper. Acid sulfate
solutions also are used for zinc, copper, and several other
metals, especially for plating relatively simple shapes.
10
-------
Barrels are used for small parts that, tumble freely in rotating
barrels. Racks are to be used for larger parts that cannot be
tumbled without surface impingment. Perforated plastic barrels
range in diameter from 15 to 75 cm (6 to 30 in«)f depending on
part size and shape. Direct current loads up to several hundred
amperes are distributed to the parts being plated in horizontal
barrels through danglers suspended from a current carrying bar
located at the longitudinal axis. In oblique barrels, a
conductive button at the bottom transmits the current.
Rack plating is required for perhaps 90 percent of the surface
area processed commercially? the parts are attached to plastic-
coated copper frames designed to carry current equitably to a few
hundred small parts, several medium-sized shapes or just a few
large products through spring-like rack tips affixed to the rack
spines. Racks fabricated for manual transfer from cleaning,
plating and rinsing tanks usually contain 2 to 7 kg (5 to 15
pounds) of parts having a surface area of 0.5 to 1 sq meter (5 to
10 sq ft). Larger racks for holding heavier parts are
constructed for use with mechanical hoist and transfer systems.
Mechanized transfer systems for both barrels and racks, which
range in cost from $50,000 to more than $1,000,000 are being
utilized for high-volume production involving six to thirty
sequential operations. In some instances, dwell time and
transfer periods are programmed on magnetic tape or cards for
complete automation.
Electroplating facilities vary greatly in size and character from
one plant to another. The size of a single facility expressed as
plating solution volume ranges from less than (100 liters (100
gallons) to more than 190,000 liters (50,000 gallons) . The area
of the products being electroplated in these facilities varies
from less than 10 to more than 1000 sq meters/day (100 to 10,000
sq ft/day). The power consumed by a single facility varies from
a few kilowatt hours/day to as much as 20,000 kilowatt-hours/day.
Products being plated vary in size from less than 6.5 sq cm (1 sq
in.) to more than 1 sq meter (10 sq ft) and in weight from less
than 30 g (1 oz) to more than 9000 kg (10 tons), continuous
strip and wire are plated in some plants on a 24-hour/day basis.
Some companies have capabilities for electroplating ten or twelve
different metals and alloys, but other specialize in just one or
two. Because of differences in character, size and processes,
few similar plants exist at the present time. Construction of
facilities has been tailored to the specific needs of each
individual plant, but the technologies used are the same across
the industry.
11
-------
SECTION IV
INDUSTRY CATEGORIZATION
Intro duct, ion
This section discusses in de-tail -the scope of the metal finishing
industry. The rationale is developed for considering the
electroplating industry as a separate subcategory for the
development of effluent limitations guidelines and standards of
performance. Further rationale is offered for the selection of
copper, nickel, chromium, and zinc electroplating for study in
Phase I and all other metal electroplating in Phase II. The
rationale is then developed to show why further subcategorization
of the electroplating industry is not required for the purpose of
developing effluent limitation guidelines and standards of
performance.
Objgctives^of^Categorization
A. primary purpose of industry categorization is to develop
quantitative effluent limitations and standards of performance
that are uniformly applicable to a specific category or
subcategory. This does not preclude further classification
within a category for the purpose of monitoring to insure
compliance.
The Relationship of Electroplating_and Metal Finishing
Electroplating is one of several processes in the broader
category of metal finishing, which includes anodizing, bright
dipping, buffing, coloring, conversion coating, descaling,
electropolishing, galvanizing, mechanical polishing, tumbling,
and other finishing processes. One, several, or all of the above
processes may be performed in a single facility.
Profile of Production Processes
The electroplating industry utilizes chemical and electrochemical
operations to effect an improvement in the surface properties of
metals and other materials.
In one segment of the industry, identified as No. 3*71 in the
Standard Industrial Classification (SIC) Manual 1972, published
by the Executive Office of the President (Bureau of the Budget),
processes are performed on metals or other materials as products
owned by a second party. Such work is done in job shops, also
known as contract shops. The same operations for electroplating
are performed by manufacturers classified by other SIC numbers,
on their own metals, materials, and products in captive shops
under their own management. Typical processes are the same for
Preceding pap Wank
-------
both types of facilities. Examples are shown for copper, nickel,
chromium, and zinc plating which is the subject of this report
according to basis metal or material and operations in Tables 3
to 7. Not shown in these tables are sequences for electroplating
cadmium, brass, gold, iron, lead, silver, tin, the platinum
metals, and other metals and alloys which are practiced by only a
few companies, relative to the much larger number engaged in
electroplating copper, nickel, chromium, and zinc. These less
common electroplating processes will be examined and analyzed
later during Phase II of this program. Copper, nickel, chromium,
and zinc plating processes which is the subject of this report
were selected first, because a large proportion (about two
thirds} of the waste generated by electroplating processes are
derived from those associated with copper, nickel, chromium, and
zinc. Furthermore, almost all facilities are equipped for
plating at least one of these common metals.
An electroplating process includes a succession of operations
starting with cleaning in alkaline solutions, acid dipping to
neutralize or acidify the wet surface of the parts, followed by
the steps of electroplating, copper, nickel, chromium, or zinc.
These operating solutions are the sources of pollutants which
appear in the rinses immediately following the concentrated
solutions, in spills, and from the discard of spent or
contaminated solutions. The intermediate rinses are essential
for removing the processing solution from the workpieces so as to
avoid contaminating the next processing solution. The final
rinse assures a clean finished surface.
Some generalizations will be encountered as process descriptions.
For example, decorative chromium plating refers to copper plus
nickel plus chromium plating and hard chromium plating refers to
only chromium (usually on steel), as seen in Table 3«
In some facilities, vapor degreasing with tri- or per-
chloroethylene precedes the alkaline cleaner. The only water
associated with this operation is for cooling. The cooling water
effluent is usable for rinsing after the alkaline cleaning.
Therefore, no further mention is made of vapor degreasing.
However, it is a source of possible air pollution.
For each typical electroplating operation, exemplified in Tables
3 to 8, a variety of solutions can be selected. The choice is
usually based on personal knowledge and experience in a specific
process for a specific basis material. The selection of an
alkaline cleaner for a specific basis material could be made from
at least five types.
Further evidence of the complex character of the electroplating
industry is seen'in the size range of less than 400 liters (100
gallons) to more than 190,000 liters (50,000 gallons) of plating
solutions in a single facility. The less than 400 liter (100
gallon) installations involve parts either small in size or
14
-------
TABLE
PROCESSES FOR PLATIHG OS STEEL
Alkaline clean/
rinse
Acid dip/rinse
Copper strike/
rinse
Acid dip/rinse
Copper/rinse
Semibrlght nickel/
rinse
Bright nickel/
rinse
Anodic treat/
rinse
Chromium/ rinse
Zinc rinse
Chrosate/ rinse
Decorative
Chromium
Plating
1
X
X
X
X
X
X
X
X
Decorative
Chromium
Plating
2
X
X
X
X
X
Hard
Chromium
Plating
3
X
X
X
X
(topper
Cladding
4
X
X
X
X
X
Protective
Zinc
Plating
5
X
X
X
Protective
Zinc
Plating
6
X
X
X
X
Carburizing
Resist
7
X
X
X
•=*
Protective
Nickel
flat ing
8
X
X
X
-------
TABLE 4 PROCESSES FOR PLATING ON ZINC DIE CASTINGS
Operation
Alkaline clean/
rinse
Acid dip/rinse
Copper strike/
riase
Acid dip/rinse
Copper /rinse
Nickel/rinse
Nickel/ rinse
Anodic treat/
rinse
Chromium/ rinse
Chromate/rinse
Decorative
Chromium
Plate
1
X
X
X
X
X
X
X
Decorative
Chromium
Plate
2
X
X
X
X
X
X
X
X
Protective
Finish
3
X
X
X
Protective
finish
4
X
X
X
X'
16
-------
TABLE 5. PROCESSES FOR PLATING ON BRASS
Operation
Alkaline clean/
rinse
Acid dip /rinse
Copper strike/
rinse
Acid dip /rinse
Copper/rinse
Nickel/rinse
Nickel/rinse
Anodic treat/
rinse
Chromium/ rinse
Chromium
Plate
1
X
X
X
X
X
Decorative
Chromium
Plate
2
X
X
X
X
X
Decorative
Chromium
Plate
! 3
X
X
X
X
X
X
Protective
Nickel
Plate
4
X
X
X
X
X
17
-------
TABLE
PROCSSSES FOR PLATING ON AtUHIKUH
Operation
Alkaiitt*
Clean/rlnae
Acid dip/ rinse
Activate/ rinse
Zinc strike/
rinse
Copper strike/
rinse
Copper/rinse
Hickel/rinse
Hickel/ria»e
Chromi'W rinse
Zinc/rinse
Chromate/rinse
Decorative
Chromium
n*te
1
X
X
X
X
X
£
X
X
Decorative
Chromium
PUt*
2
X
X
X
X
X
X
z
X
. X
Decorative
Chromium
Place
3
X
X
X
z
Protective
Zinc
Plate
4
X
X
X
X
X
X
TABLE 7 PBDdSSlS FOR PIATIHO OH PLASTICS
Operation
Alkaline
Clean/rinse
Acid dip rinse
Activate rinse
Catalyze rinse
Eleccroaess
Deposit/rinse
Copper scrike/
rinse
Copper/rinse
Nickel/rinse
Nickel/rinse
Chromiusi/rinse
Decorative
Oiroaiuts
Plate
1
X
X
X
X
X
X
X
X
X
Decorative
Chromium
Plat*
2
X
X
X
X
X
X
X
X
X
Sasis
for
Ccatlng
3
X
X
X
X
X
X
X
Basis for
Magnetic
Coating
4
X
X
.X
X
X
X
18
-------
quantity or specialized such electrodepositing chromium on tools
and custom parts in a captive shop. Installations of larger
volumes process parts large in size such as bumpers for
automobiles, sheet and strip steel for prefab plating and/or
large numbers of zinc die castings and steel and brass stampings
or castings.
At the low and intermediate region of the size range are the
contract shops, representing approximately 3500 facilities of SIC
3471 classification. Larger facilities are in captive shops
where logistics and process control are more effectively geared
to a high production volume. Other SIC classification numbers
cover the captive plating facilities, estimated to be five to six
times the number of contract or job shops, About 90 percent of
the volume of electroplating in dollars-added value is supplied
by companies doing -their own electroplating on their own
products.
Unlike most of the captive plating operations, which process
approximately the same number of the same products each month,
job shops are required to handle a greater variety of shapes and
different metal substrates. Production volume for a specific
type of product varies appreciably from day to day. Thus, an
individual job shop might be generating a large amount of copper,
nickel, and chromium waste and little or no zinc waste during a
limited, three- or four-week period at the beginning of a new
model-year season for automotive or appliance hardware, or a much
lesser amount of copper, nickel, and chromium waste and a large
amount of zinc waste near the end of a model-year run for typical
customer products. Day-to-day variations can be expected in the
amount and type of waste generated by a typical independent
facility as a result of meeting agreed on delivery schedules.
Because of the large variety of products handled by the
independent job shops, in-process controls for minimizing waste
are less effective, in comparison with the controls that can be
exercised in a captive facility always processing the same
products and materials. As a result of this situation, the
advent of rigid waste-discharge enforcement is expected to
encourage some degree of specialization among the independent
job-shop establishments. Such a trend will reverse the tendency
established in the past by companies that have expanded in
facilities with a larger number of electroplating and finishing
processes in order to provide improved service to industry in a
given geographical area.
Regardless of the size of facility for copper, nickel, chromium,
and/or zinc electroplating, it will process one or more of the
commonly used basis materials: steel, zinc die castings, brass,
aluminum, and plastic such as &BS and polypropylene as summarized
in Tables 3 to 7, The distribution of electroplating according
19
-------
to basis material is shown in Table 8. More than half of all
electroplating is done on steel as a basis material. Zinc alloys
as die castings comprise the next largest category of basis
materials. Reference to Tables 3 to 6 shows that basis materials
are first cleaned and acid dipped prior to the first
electroplating step.
TABLE 8. DISTRIBUTION OF ELECTROPLATE ACCORDING
TO TYPE OF BASIS MATERIAL
Plate
^ .
steel zinc Die Cast Brass Aluminum Plastics
Copper
Nickel
Chromium
Zinc
50
48
54
100
46
44.9
33.9
2
5 0.1
4 0.1
2
2
2
Factors.Considered in Categorization
When the nature of the industry and the operations performed were
analyzed, consideration was given to the further categorization
of electroplating according to one or more of the following:
(1) Type of basis material
(2) Product design
(3) Raw materials used
(4) Size and age of facility
(5) Number of employees
(6) Geographic location
(7) Quantity of work processed
(8) Waste characteristics
(9) Treatability of wastes
(10) Rack plating versus barrel plating.
20
-------
Type of Basis Material
The wastes produced by processing all common basis materials are
similar. A single facility can process all basis materials
without significant change in the raw materials consumed or the
waste-treatment technique adopted for control of end-of-pipe
water discharge. Although it is possible that the basis material
may contribute to the waste stream when alkaline cleaned and acid
dipped, it is an insignificant quantity when compared to the
waste generated from the plating solutions by the rinsing of the
plated object. Any materials dissolved from the surface of the
customary basis metals during processing are removed from
wastewater discharge by the treatment processes adopted for
removing copper, nickel, chromium and zinc, which are described
in Section VII, Furthermore, the basis materials selected for
most consumer products frequently are interchanged from one model
year to another. Therefore, the type of basis material does not
constitute a basis for subcategorization.
Product Design
Although complex shapes tend to generate more waste than simpler
ones,, the premium in costs for fabricating and plating the
complex shapes far overshadows any small supplemental waste-
treatment cost for such products. Product design precepts for
minimizing electroplating costs also reduce wastes created by
electroplating processes (1). Furthermore, the in-process
controls and rinsing techniques described in section VII for
minimizing the wastes generated by copper, nickel, chromium, and
zinc electroplating processes have been adopted for canceling the
effect of the shape factor. Therefore, product design variance
is not a basis for subcategorization.
Raw Materials Dsed
Raw materials do not provide a basis for subcategorization,
because practicable waste-treatment technology identified in
section VII is equally applicable to all of the usual procedures
and solutions described previously for electroplating copper,
nickel, chromium, and zinc. In any facility carrying out one or
more of the processes shown in Tables 3 to 12» the same waste-
treatment needs arise. such variations as exist for each
operation are not unique and do not affect the waste-treatment
technology and control.
21
-------
PROCESSING SEQUENCES DECORATIVE COWEfc-MICKEL-CHROttlUH PLATIBG
t-O
N3
Required Process
(1) Oil and grease removal
(2) Scale removal
(3) Pretreatoient
(4) Prep late
(5) Copper plate
(6) Nickel plate
(7) Chronfum plate
Low Carboa
Be grease
Acid pickle
rinse
Soak clean
rinse
Anodic
-------
. TABU 10 H50CESSI8G SIQOEBCES Bffi SICKS PLATIMC
IO
to
Required Process
(1) Oil and grease removal
(2) Scale renoval
O) fre treatment
(4) PrepUce
(5) Nickel plate
Steel*
CSit COBCBI and Zinc Di« Aluminum and NirV.1 and
Low Carbon High Carbon Stainless Iron Its Alloy* Castings Its Alloys Its Alloys
Degreaae Be grease T>e grease Begrease Degress* Degresse Begrea»e Degreas*
Acid pickle Anodic pickle 1IN03/I!F Keehaai- Acid of cya- Mechanical Bright dip Fickle rinse
rinse rinse rinse anodic nle rlnae
pickle
rinse
Klckel strike Nickel sttrik* Activate Nickrl -- Cu-ntrike Cu-strike Nickel strike
anodic strike Cyanide copper rinse
cathodie rime Acid dip rios*
Acid dip rinse
Acid copper
rlnae
Wott. nickel
Scraibrlght nickel ,
Bright nickel | foe all feaae «wt«ls
Any one or any
combination thereof
TABLE 1 1 PROCESSING SEQUENCES JTOI CHSQMIUM PLATING
Required Process
(1) Oil and grease removal
(2) Scale removal
(3) Prttteatment
(4) Prepl.t.
(S> Plate
Low Carbon
Decrease
, Acid pickle
rinse
Anodic clean
rinse
A&cxlic chronic
acid
--
--
Hsid chronium
riTuo
Hot rinse
Steels
High Carbon
Degrease
Anodic pickle
rinse
Anodic clean
rinse
Anodic chronic
acid
~
—
Hard enroolun
rinse
Rot rlnae
Stainless
Degrease
HN03/HF rinse
Soak clean
rinse
Anodic clean
rinse
Acid dip rinse
or anodic in
chronic acid
..
Decorative or
hard chroraiua
rinse
Rot rinse
Cast
Iron
Degrease
Mechanical or
anodic pickle
Anoaic clean
rinse
Anodic in
chronic acid
Chrome flash
Hard chromiun
rime
Rot rinse
Copper «nd
Its Alloy*
Degreaae
Acid or cyanida
dip rinse
Catbodic clean
Anodic clean
rinse
Acid dip rint»
«
Decorative
chromium
rinse
Hot rinse
Zinc Dl«
Castings
Degrease
Mechanical
rinse
Sequence "A"
only
Decorative
chrotnlua
rinse
Hot rtnie
Alwiinum and
tti Alloys
Degrease
Bright dip
rinse
Soak clean
rinse
Cat hod ic etch
ritise
Acid dip tins*
or sequence
"A"
Copper
Decorst ive
chtonlua
rinse
Hot rinse
HUkel and
Its Alloys
Be grease
Mckle rinse
Sequence "A"
Copes r or
nickel
Decorative
ehrorae
rinse
Hot rinse
-------
TABLE 1 2 PROCESSING SEQUENCES »OR ZINC PLAXIHG
Required Process
(1) Oil and grease removal
(2) Scale removal
(3) Pretreatment
(4) Preplate
<5) Mate
(6) Posttreattnent
Steels
Lew Carbon
Decrease
Acid pickle
rinse
Soak clean rinse
Anodic clean rinse
Cyanide dip rinse
—
High cyanide zinc or
low cyanide zinc ^
or acid eine or j-
zinc fUioborate
rinse
Acid bright dips
Acid rinse ,
Chromate conversion r
coatings rinse
Hot rinse
High Carbon
Degrease
Anodic pickle
rinse
Soak clean
Cathodic clean
rinse
Acid dip or
anodic acid
rinse
Copper strike or
acid zinc
strike rinse
Caet Copper and Aluminum and
Iron Its Alloys Its Alloys
Degrease Eegreaae Degrease
Kecrumicul or Acid or cyanide Bright dip
anodic pickle dip rinse rinse
rinse
Soak clean Sequence "A" Sequence "A"
Cathodic clean
rinse
Acid dip or
anodic acid
rinse
Copper strike OT Copper strike
acid zinc rinse*
strike rir.se
for all base metals
for all base netala
* For soldered parts only.
-------
Size and Age of Facility
The nature of electroplating is the same in all facilities
regardless of size and age. For example, copper plating is
technically the same in 190 liters (50 gallons) as in 19,000
liters (5,000 gallons) or larger installations. Technically, the
age of the facility does not alter this situation.
Electroplating of nickel, chromium, and zinc follows the same
pattern. Thus, the characteristics of the waste will be the same
for plants of all ages and sizes. Only the quantity of waste per
unit time will differ. Yet, this factor is not a basis for
subcategorization, because waste discharge after treatment is
directly proportional to the size of the facility expressed as
amount of metal deposited, as shown in Figure 1. The amount of
metal deposited in typical facilities is directly related to the
current consumed for plating, the number of liters of installed
plating solution, and the volume of production. The guidelines
recommended in this document provide for variable production
volume with no need to differentiate plant capacity as a
subcategory.
It is recognized that some small plating facilities may have
insufficient space for accommodating effective in-process
controls for minimizing water use and/or conventional chemical
waste treatment equipment. The capital investment/burden for
installing good waste control may be greater for such small
companies relative to the burden that can be amortized by larger
companies. In such cases, heavy metal pollutants can be absorbed
on the resins in small ion-exchange units available at relatively
modest investment. At least one vendor of such equipment will
replace the resin beds, back wash the used beds in their own
facilities and regenerate the resins for reuse. Alternatively,
both local and regional organizations equipped with large tank
trucks supply a hauling and treating service in several areas.
It is also possible that a small electrodialysis system would
provide recycling of cyanide, costs depend on water volume and
the concentration of pollutants. However, because of economic
reasons, shops plating less than 33 sq m/hr or having an
installed current capacity of less than 2000 amperes are required
only to destroy the cyanide, equalize and pH adjust their waste
prior to discharge.
Number of Employees
The number of employees engaged in electroplating does not
provide a basis for subcategorization, because electroplating
operations can be carried out manually or in automatic machines
which greatly conserve labor. For example, an operation with
3,785-liter (1,000-gallon) processing tanks may require six
people if operated manually, whereas a plant of the same tank
size and carrying out the same operations in an automatic machine
would need only two people. The same amount of waste would be
generated in each case, if the products being plated were equal
in total area. Other examples could be cited to show that no
basis exists for relating the number of employees to the
25
-------
Production Capacity, Lb Metal Deposited/Hour
20 40 ' 60 80
0,20
QI5
s
o
0)
I
0.10
0.05
(40-6^(36-1)
133-20)
156-2) |
(11-8)
(33--I)
(33-6)
100
0.4
0.3 S
0.2
"a
I
O.I
10 20 30 40
Production Capacity, Kg Metal Deposited/Hour
FIGURE 1, RELATIONSHIP OF TOTAL METAL IN TREATED
WATER DISCHARGE TO THE PRODUCTION
CAPACITY OF TYPICAL ELECTROPLATING
PLANTS EXPRESSED AS METAL DEPOSITED
PER HOUR
26
-------
electroplating operations carried out and/or to the waste that
results from those operations.
Geographic Location
Geographic location is not a basis for subcategorization. No
condition is known whereby the choice of electroplating
operations is affected by the physical location of the facility,
except availability of process water. If water is not available,
no modification of electroplating procedures can compensate for
this lack. No electroplating facilities would be installed at a
water-deficient location, because large amounts of water are
required for replacing water lost by evaporation. The waste-
treatment procedures described in Section VII can be utilized in
any geographical area. In the event of a limitation in the
availability of land space for constructing a waste-treatment
facility, the in-process controls and rinsewater conservation
techniques described in Section VII can be adopted for minimizing
the land space required for the end-of-process treating facility.
A compact unit can easily handle end-of-process waste if the best
in-process techniques are utilized to conserve raw materials
and/or water consumption.
Quantity of Work Processed
Quantity of work processed is analogous to plant size.
Therefore, the discussion about plant size is equally applicable
to the quantity of work processed. The application of the
guidelines provides for the production of a particular facility.
Waste Characteristics
The physical and chemical characteristics of all wastes generated
by copper, nickel, chromium, and zinc electroplating processes
are similar. Specifically, all wastes are amenable to the
conventional waste-treatment technology detailed in Section VII.
The characteristics of treated waste are the same througout the
industry. Thus waste characteristics do not constitute a basis
for subcategorization.
Treatability of Wastes
As no peculiarity exists between raw materials and waste
characteristics as a basis to separate facilities into
subcategories, none exists for treatability of wastes as a basis
for subcategorization. All of the principal treatment procedures
and in-process controls are technically applicable by choice for
any given waste and all operations generate the same type of raw
waste regardless of the facility.
27
-------
Rack Plating Versus Barrel Pla-ting
The choice of rack or barrel methods for plating is based on the
size and quantity of the parts to be processed per unit of time.
Neither of these conditions imposes a significant technical
change in the operations for electroplating. The selection is
always based on economic considerations because hand racking of
small parts is usually more costly than barrel processing in
bulk. Sometimes plating bath compositions will be modified by
altering the concentration of solution constituents. However,
the same types of salts, acids, and additives will be used.
Thus, the impact on waste characteristics is not changed. The
volume of wastewater (dragout) is frequently greater in barrel
plating operations but the final effluent quality is not a
function of influent concentration. Technigues are available to
reduce the rinse water volumes in barrel plating to the levels of
rack plating. These techniques are detailed in Section VII,
Therefore, rack plating and barrel plating are not appropriate
subcategories.
28
-------
SECTION V
WASTE^CH^A^TERIZATION
Int.rQdiact.iQn
Water flow and the sources, nature and quantity of the wastes
dissolved in the water during copper, nickel, chromium, and zinc
plating processes are described in this section. Water is a
major material in the electroplating industry and is associated
with every operation. Yet, none of the water enters the product.
Specific Water Uses
Water is used in the following ways:
(1) Rinsing to remove films of processing solution from the
surface of work pieces at the site of each operation
<2) Washing away spills in the areas of the operations
(3) Washing the air that passes through ventilation ducts so
as to remove spray from the air before it is exhausted
(4) Dumps of operating solutions, mostly pretreatment and
posttreatment solutions
(5) Rinse water and dumps of solutions from auxiliary
operations such as rack stripping
(6) Washing of equipment (e.g., pumps, filters, tanks)
(?) Cooling water used in heat exchangers to cool solutions
in electroplating processes.
Rinsing
fi. large portion (perhaps 90 percent) of the water usage is in the
rinsing operations. That used as cooling water is usually reused
for rinsing. The water is used to rinse away the films of
processing solutions from the surface of the work pieces. In
performing this task, the water is contaminated by the operating
solutions and is not directly reusable. Thus, the cost of water
is an operating expense. Aqueous solutions result from the raw
waste from each operation. Therefore, the location of rinse
steps is important relative to the operations performed in the
electroplating process. The general outline of operations in the
processes was given in Tables 3 to 7.
Figures 2 and 3 schematically illustrate the flow for work pieces
being processed and show the sites of water usage for rinsing.
Figure 2 shows the minimum number of operations and the water
flow in the wide practice of decorative chromium plating.
However, there is no fixed relation between water usage and
amount of work processed. Some plants use more water than the
minimum required to maintain good quality work.
29
-------
Work flow
Sludge
Precipitate
nickel and copper
Treated water <
FIGURE 2. SCHEMATIC FLOW CHART .FOR WATER FLOW IN CHROMIUM
PLATING ZINC DIE CASTINGS, DECORATIVE
30
-------
Clean water
one or two rinses
Work flow
a. One or Two (SeriesJ Rinses
Clean water
Work flow]
Effluent water
Sludge
b. Two Counter-Flow Rinses
Clean water
c. Three Counter Flow Rinses
FIGURE 3. ALTERNATIVE METHODS OF RINSING AFTER A PROCESSING OPERATION
31
-------
Tables 3 to 7 show other processes which have an analogous water
use for each operation of cleaning, acid dipping, plating, and
rinsing according to one of the schemes in Figure 3.
Spills and Air Scrubbing
The water from washing away spills and washing down ventilation
exhaust air is added to the chemically corresponding rinse water
for treatment.
Dumps
Operating solutions to be dumped are slowly trickled into rinse
water following the operation and prior to treatment.
Alternatively, the operating solutions, which are much more
concentrated than the rinse water, may be processed batch-wise in
a treating facility. Subsequent discussion of waste treatment of
rinse water covers all the water in the facility.
Water from Auxiliary Operations
Auxiliary operations such as rack stripping utilize solutions
containing acids or cyanide for removing metal deposited on rack
tips. These solutions accumulate large concentrations of metals
and are decanted or dumped at regular intervals. They should be
slowly trickled into the appropriate rinse water stream that
contains similar chemicals for ultimate treatment.
Washing Equipment
Water used for washing filters, pumps, and tanks picks up
residues of concentrated solutions or salts and should be routed
to the appropriate rinse water stream for chemical treatment.
Cooling Water
As noted previously cooling water used in heat exchangers for
cooling electroplating solutions is usually routed to rinse tanks
for water conservation purposes. If this practice is not
adopted, exit water from cooling units should be checked for
constituents of the plating solution to guard against the
discharge of pollutants in the event of a leak into the cooling
unit.
Quantity_ofWastes
At least 95 percent of the products being electroplated (or
electroformed) to provide resistance to corrosion, wear, and
other destructive forces are processed in medium sized or large
32
-------
plants (4,000 to 5,000 in number), each deploying at least 11
kg/day (25 pounds/day) of raw waste into rinse water. The
potentially toxic waste in the form of heavy metal salts and
cyanide salts from these sources is approximately 340,000 kg/day
(750,000 pounds/day) . This is equivalent to about 110,000 kg/day
(250,000 pounds/day) of heavy metal and cyanide ions. Of the
total salts, about two-thirds or 228,000 kg/day (505,000
pounds/day) is contributed by copper, nickel, chromium, and mine
plating operations, as shown in Table 13.
Supplementing the chemicals listed in Table 13, at least 225,000
kg/day (500,000 pounds/day) of alkalies and 450,000 kg/day
(1,000,000 pounds/day) of acids are contributed to the total
waste by cleaning and pickling operations that precede copper,
nickel, chromium, and zinc plating. The proportion of phosphates
in alkaline cleaning chemicals is unknown, but is believed to be
25 percent of the total alkalies.
Some of the alkaline solution waste and nearly all of the acid
solution waste contain metals resulting from the dissolution of
metal products to be plated. Hence, the total amount of
wastewater constituents generated by copper, nickel, chromium,
and zinc electroplating probably exceeds 900,000 kg/day
(2,000,000 pounds/day).
From the estimated plating salts in Table 13, the total metal and
cyanide load was estimated as follows:
Copper 11,000 kg/day ( 24,000 pounds/day)
Nickel 12,000 kg/day ( 27,000 pounds/day)
Chromium 25,000 kg/day ( 55,000 pounds/day)
Zinc 19,000 kg/day ( 42,000 pounds/day)
Cyanide ^46^000 kg/day (102,000 pounds/day)
TOTAL Il3,000 kg/day (250,000 pounds/day)
The estimated alkali load of 230,000 kg/day (500,000 pounds/day)
and acid load of 450,000 kg day (1,000,000 pounds/ day) are
usually in about the same ratio in most plants (i.e., combined
acid/alkali wastewaters are mostly acid). Assuming the
alkalinity as sodium hydroxide (NaOH) and acidity as sulfuric
acid (H,2SQ4), combination/neutralization (about 0.9 kg NaOH/kg
HT2SO4) would indicate a total net acid load of 350,000 kg/day
(7507000 pounds/day) .
Sources_of_waste
In electroplating facilities the wastes are derived from the
material plated (discussed in Section IV) and the operating
solutions. The principal ionic constituents of wastewater from
plating on five basis materials are listed in Tables 14 to 18.
Wastes associated with preparation for plating, electroplating,
and postplating are combined in these tables. These operations
are discussed below in more detail.
33
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TABLE 13. ESTIMATED DAILY RAW WASTE LOAD OF PRINCIPAL SALTS
USED IN COPPER, NICKEL, CHROMIUM, ZINC PLATING
AND RELATED PROCESSES^a)
Principal Salts
Operation
Identity
kg/day pounds/day
Percent of
Total Salts
Consumed by
Plating
Copper plating
Nickel plating
Chromium plating
Zinc plating
Copper cyanide, 54,000
sodium cyanide, and
copper sulfate
120,000
Nickel chloride and
nickel sulfate
Chromic acid
Zinc oxide, zinc
cyanide, sodium
cyanide, and
zinc sulfate
54,000 120,000
45,000
68,000
100,000
150,000
(a) Data from a survey conducted by Battelle's Columbus
Laboratories in 1965.
13
17
13
23
Zinc
chromating
Sodium
sodium
ehromate and
dichromate
6
227
,800
,800
15
505
,000
,000
2
68
34
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TABLE 14, PRINCIPAL WASTEWATER CONSTITUENTS IN
WASTES MOM PROCESSES FOR PLATING
ON STEELS*
Constituent
Iron, ferrous, Fe"*"2
1 1
Copper, cuprous, Cu i
Copper, cupric, Cu*"2
Nickel, Hi+2
Chromium, chromate, Cr**>
Chromium, chromic, Cr~"
Zinc, Zri*"2
Cyanide, CN"1
Sulfate, S04'2
Chloride, Cl"1
Carbonate, 003 ~2
Silicate, SiOs"2
Phosphate, FO^
Fluoborate, BFs"^
Sulfamate, NH2S03"!
Nitrate, NOg""^
Organics
1
X
X
X
X
X
X
X
X
X
X
X
X
2 3
X
X
X
x!
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
4
X
X
X
X
X
X
X
X
X
X
5
X
X
X
X
X
X
X
X
6
X
X
X
X
X
X
X
X
X
J
7
X
X
X
X
X
X
X
X
X
X
8
X
X
X
X
X
X
X
X
* Process numbers correspond to those in Table 2.
35
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TABLE 15. PRINCIPAL WASTEWATER CONSTITUENTS
IN WASTE FROM PROCESSES FOR MATING
ON ZINC DIE CASTINGS*
Constituent
Fe+2
Cu+1
Cu+2
HI"*"2
Cr+6
Cr+3
Zn+2
CN"1
S042
cr1
C03~2
SiOs"2
P04*3
-l
BF6 L
Organics
1
X
X
X
X
X
X
X
X
X
X
X
2
X
X
X
X
X
X
3
X
X
X
X
X
X
4
* Processes correspond to those in Table 3.
36
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TABLE 16, PRINCIPAL WASTWATER CONSTITUENTS
IN WASH FROM PROCESSES FOR PLATING
ON BRASS*
Constituent
Cu+2
Ni+2
Cr+6
Cr+3
Zri*2
CN"1
ci-i
C03"2
SiOs"2
P04"3
BF6"1
NH2S03"1
NH3+1
Organics
1
X
X
X
X
X
X
X
X
X
X
X
X
2
X
X
X
X
X
X
X
X
X
X
X
3
X
X
X
X
X
X
X
X
X
X
X
X
4
X
X
X
X
X
X
X
X
X
* Processes correspond to those in Table 4.
37
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TABLE 17. PRINCIPAL WAS THEATER CONSTITUENTS IN
WASTE FROM PROCESSES FOR PLATING ON
ALUMINUM*
Constituent
Fe+3
Cu+2
jjj+2
Cr"1"6
Cr+3
2n+2
A luminum , A IT*"3
CN"1
S04"2
Cl"1
cos"2
Si03"2
P04"3
BFg'1
NH2S03"1
Organics
1
X
X
X
X
X
X
X
X
X
X
2
X
X
X
X
X
X
X
X
3
X
X
X
X
X
X
X
4
5
* Processes correspond to those in Table 5.
38
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TABLE 18. PRINCIPAL WASTEWATER. CONSTITUENTS
IN WASTE FROM PROCESSES FOR PLATING
ON PLASTICS*
Constituent
Tin,
Palladium,
Organics
Fe+3
Cu+2
Nit2
Cr+6
Cr+3
Sn+2
Pd+2
S04"1
el'1
C03"2
Si03"2
PO^
_1
BF6 l
NC^"1
1
X
X
X
X
X
X
X
X
X
2 j 3
X X
X X
X i
X
X X
X X
X
X
X
X
X
X
4
X
X
X
X
X
X
* Processes correspond to those in Table 6.
39
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Preparation for Plating
Wastewater constituents derived from the chemicals generally
utilized for preplate preparation solutions or from reactions
with the common basis materials processed in these solutions are
as follows:
Alkyl aryl oxyalcohols
Alkyl aryl sulfonates
Aluminum chloride
Aluminum nitrate
Aluminum sulfate
Chromic acid
Copper chloride
Copper fluoborate
Copper nitrate
Copper sulfate
Ferric chloride
Ferric phosphate
Ferric sulfate
Ferrous chloride
Ferrous phosphate
Ferrous sulfate
Fluoboric acid
Hydrochloric acid
Nitric acid
Phosphoric acid
Sodium bisulfate
Sodium borate
Sodium carbonate
Sodium hexametaphosphate
Sodium hydroxide
Sodium tnetosilicate
Sodium orthosilicate
Sodium pyrophosphate
Sodium sulfate
Sodium triphosphate
Stannous chloride
sulfamic acid
Sulfuric acid
Zinc chloride
Zinc sulfate
Solutions of all of -the above chemicals containing acids and
alkalies must be neutralized prior to discharge into navigable
waters. All of the metals may be removed to varying degrees by
the treatment techniques discussed in Section VII.
Alkaline_-__Cj.eaneris. Regardless of the material to be
electroplated, cleaners are made up with one or more of the
following chemicals: sodium hydroxide, sodium carbonate, sodium
metasilicate, sodium phosphate (di- or trisodium}, sodium
silicate, sodium tetraphosphate, and a wetting agent.
Compositions for steel are more alkaline and active than those
for brass, zinc die castings, and aluminum. Soils to be removed
from basis materials by cleaners are unrelated chemically to the
metal and usually are the same general type. The need for
variation in cleaner composition is partly based on the nature of
the soil and on the chemical resistance of the material being
prepared for plating.
In addition to the chemicals comprising the alkaline cleaners,
rinses and spills, wastes contain soaps from emulsification of
certain greases left on basis material surfaces from polishing
and buffing that precede electroplating. Also, emulsified oils
are likely to be present. The raw wastes from the basis
materials and process solutions prior to plating show up in the
rinse waters, spills, dumps of concentrated processing solution,
wash waters from air-exhaust ducts, and leaky heating and cooling
coils and heat exchangers.
40
-------
Acid_Di]DS. Acid dips are chosen to accommodate the basis
material, Aoid solutions are made up with one or more of the
following: hydrochloric acid, sulfuric acid, phosphoric acid,
fluoboric acid, chromic acid, and nitric acid. The solution
compositions vary according to nature of any tarnish or scale,
chemically related to the metal and to the resistance of the
material to chemical reaction with the acid solution. The acid-
treating baths for preparing metal substrates for plating usually
have a relatively short finite life. When used solutions are re-
placed with fresh solutions, large amounts of chemicals must be
treated or reclaimed. Water used for rinsing after acid treating
also collects heavy metal waste by dragout of solution from the
acid-treating tank.
Acid solutions used for pickling, acid dipping, or activating
accumulate appreciable amounts of metals, as a result of. metal
dissolution from metallic work pieces and/or uncoated areas of
plating racks that are recycled repeatedly through the cleaning,
acid treating, and electroplating cycle. In barrel Einc-plating
operations, the amount of zinc dissolved in the acid-treating
solution from the danglers used to make electrical contact to the
work pieces sometimes equals the amount of zinc carried over into
the water rinse solution following the zinc-plating bath. The
copper (and zinc) accumulated in acid bright dip solutions used
to prepare electrical copper and brass contacts for plating can
exceed in amount the metal contributed to rinse-water waste by
dragout from the plating bath.
The amount of waste contributed by preplate preparation steps
varies appreciably from one facility to another, depending on the
substrate material, the formulation of the solution adopted for
cleaning or activating the material, the solution temperature,
the cycle time, and other factors. The initial condition of the
substrate material affects the amount of waste generated during
preplate treatment. A dense, scalefree copper alloy article can
be easily prepared for plating by using a mild hydrochloric acid
solution that dissolves little or no copper, whereas products
with a heavy scale require stronger and hotter solutions and
longer treating periods to insure the complete removal of any
oxide, prior to plating.
Electroplating
wastewater constituents derived from solutions generally used for
electroplating copper, nickel, chromium, and zinc are as follows:
Alkylaryl sulfonates potassium hydroxide
Aluminum chloride Rochelle Salts
Aluminum sulfate Saccharin
Ammonium chloride sodium bicarbonate
Boric acid Sodium carbonate
41
-------
Chromic acid Sodium cyanide
Coumarin sodium ethylene diamine
Copper cyanide tetra acetic acid
Copper sulfate Sodium fluosilicate
Fluoboric acid Sodium hydroxide
Fluosilicic acid Sodium pyrophosphate
Hydrochloric acid Zinc chloride
Nickel chloride Zinc cyanide
Nickel fluoborate Zinc fluoborate
Nickel sulfamate Zinc oxide
Nickel sulfate Zinc sulfate
Potassium cyanide Sulfuric acid
Prior to end-of- process discharge, solutions containing alkalies
and acids (or acid salts) must be neutralized. All of the metals
must be removed to the specified levels by the technology
detailed in Section VII.
jPl atijig . copper is electroplated from four types of
^^
baths, I.e., alkaline cyanide, acid sulfate, pyrophosphate, and
fluoborate, which are prepared with a corresponding copper salt,
The cyanide solutions also contain sodium carbonate and may also
contain sodium hydroxide or sodium potassium tartrate, All four
types may also contain a small amount of an organic chemical for
refining the grain or brightening the plate. Typical
compositions are cited in References (2) and (3) . Cyanide
solutions are used extensively for copper plating, but acid
copper solutions have been adopted for plating large numbers of
steel, plastic, and zinc alloy products. Steel and zinc are
customarily plated first in a cyanide strike bath to insure good
electroplate adhesion. copper plating solutions are rarely
dumped, so the principal source of waste is the rinse water used
to remove the solution that remains on work surfaces (dragout)
after copper-plated articles are removed from the plating tank.
Rinsing between cyanide copper striking and plating in a
concentrated cyanide bath is not required, so facilities equipped
with both kinds of solutions create just one source of waste, in
comparison with others equipped with a cyanide strike and an acid
bath. Even so, some companies prefer the cyanide strike-acid
copper sequence for minimizing the amount of cyanide waste
requiring treatment by chemical oxidation or for improving the
quality of their products.
A secondary source of waste in a typical copper plating facility
is associated with solution filtration. Filters, pumps, and
pipes commonly develop leaks, classified as spills. Not all of
the solution is washed back into the plating tank when filter
cartridges or bags are exchanged for new ones (or washed free of
contaminating solids that reduce the filtration rate) . The high-
concentration cyanide and acid copper sulfate solutions are
usually filtered continuously, in order to prevent rough
deposits.
42
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A nickel strike for steel has been adopted by some companies
choosing to eliminate cyanide baths. The acid copper sulfate
bath can then be used over the nickel strike, in a sequence
similar to that adopted for copper plating on plastic which is
first metallized by a thin film of electroless nickel. A
satisfactory nickel strike has not been identified for zinc die
castings, which are universally plated first with a cyanide
copper strike. Copper is extensively electroplated in
combination with nickel and chromium. About 75 percent of the
copper anode consumption (18, 000,000 kg/year or J»Q,OQQ,QOQ
pounds/year) is expended for this purpose, but other applications
account for significant quantities. For example, printed circuit
boards are copper plated to make through-hole electrical contacts
between circuits on opposite sides of the boards. Another
significant activity is copper electro forming (including
electrotyping) . Some facilities installed for electroplating
cabinet hardware (principally steel and zinc alloy die castings)
utilize copper plating as the only deposition step, to produce
colored finishes .
_ Nickel is electroplated from Watts (sulfate-
chloride-boric acid), sulfamate, chloride, and fluoborate baths.
Each type of solution is prepared with the corresponding nickel
salt, a buffer such as boric acid and a small concentration of a
wetting agent. A small amount of another organic chemical may be
added to brighten the deposits or control another property.
Nickel is extensively electroplated in a three-metal composite
coating of copper, nickel, and chromium. In the best practice,
nickel plating would follow copper plating without drying as in
Processes 1 and 2, Table ^. Nickel also is electrodaposited on
steel for decorative- protective finishes and on other materials
for electrof owning. In these applications, nickel plating is
preceded by cleaning and activating operations in a sequence
selected for a specific basis material. Nickel electroplate is
freshly plated and rinsed without drying and directly chromium
plated according to processes shown in Tables 3 through 7.
Typical solution compositions are given in References 2 and 3.
In addition to the constituents of new solutions, used solutions
contain small concentrations of other heavy metals, depending on
the kind of material being processed. For example, the nickel
bath gradually picks up copper and zinc when copper-plated steel
and copper-plated zinc die castings are being nickel plated.
Only periodic analyses will reveal the amounts present.
Organic agents that refine the grain size of the deposit and
brighten the plate are added to all nickel plating baths adopted
for sequential nickel-chromium plating. Proprietary agents are
supplied by metal finishing supply companies that have developed
stable, effective chemicals for insuring mirror-like, corrosion-
protective deposits requiring no buffing. Aryl polysulfonates,
sulfonamides, and sulfinimides such as napthylene disulfonic
acid, p-toluene sulfonamide, and saccharin are examples of one
class of brightening agents frequently combined with a sulfonated
aryl aldehyde, ethylene sulfonamide, amine, nitrile, imide, azo
43
-------
dye, or another special compound. These organic chemicals and
the surface active agents (typically sodium lauryl sulfate)
customarily added to reduce surface tension and prevent pitting
contribute small concentrations that impose a small COD to the
•water rinse step following nickel plating. Because the organic
compounds are customarily added to nickel plating baths in small
concentrations (0.5 to 3 g/1), their total concentration in the
untreated rinse water seldom exceeds 4 mg/1.
Leakage from filters, pumps, and pipes is a secondary source of
nickel waste, although some filters are equipped to recover and
recycle leaks that occur from the pump and filter. Incomplete
washing of filter cartridges, bags, or plates during filter
maintenance is another source of waste. Continuous filtration of
the nickel solution is adopted for preventing roughness by most
of the ;companies engaged in nickel plating. Filters sometimes
are packed with activated carbon for removing organic impurities
that degrade the characteristics or properties of the deposit.
the relatively high value of nickel has encouraged the adoption
of in-process controls for minimizing dragout into the rinse
water following nickel plating, which is the major source of
waste. Nickel plating baths are rarely dumped.
Chromium^ Plating. All chromium plating solutions contain chromic
acid and a small amount of sulfuric acid or a mixture of sulfuric
acid and fluosilicate or fluoride ions. The concentration of
chromic acid .usually is two orders of magnitude higher than the
concentration of the other materials. Three basis materials
account for the * bulk of the works steel, nickel-electroplated
steel, and nickel-electroplated zinc. Solutions containing 150
to 400 g/1 of chromic acid are the common baths for
electroplating 6.2 to 1.0m (0.000008 to 0.00040 inch) of
decorative chromium or hard chromium on steel and aluminum for
resisting wear. Unlike the copper and nickel plating processes
which; ' utilize soluble copper, or nickel anodes to replenish in
solution the metal deposited on the work pieces, chromium plating
processes always use insoluble lead alloy anodes. Thus, some
portion of the chromic acid added regularly for maintenance is
consumed by reduction to chromium metal at cathode surfaces.
This proportion varies from only 10 to 20 percent in decorative
chromium plating facilities to the range of 25 to 90 percent in
hard chromium installations, depending on the in-process controls
adopted for reducing the dragout loss to the rinse water.
Dragout into rinse water is the major source of raw waste. Spray
carried from the solution by the hydrogen gas generated at
cathode surfaces and oxygen gas produced at anode surfaces is a
significant secondary source. Chromium plating process tanks are
customarily vented to protect workers from this spray, so an
appreciable amount of chromic acid is carried into air ducts in
the form of aerosols released to the atmosphere. Air scrubbers
are incorporated in tthe exhaust systems installed in some plants
to recover this s'otirce of waste and recycle it to the chromium
plating bath.
44
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Zinc Plating. Zinc is electroplated in cyanide solutions
containing sodium cyanide, zinc oxide or cyanide and sodium
hydroxide; noncyanide alkaline solutions prepared with zinc
pyrophosphate or another chelating agent such as tetrasodium
pyrophosphate, sodium citrate or the sodium salt of ethylene
diamine tetraacetic acid; acid or neutral chloride baths prepared
with zinc chloride and a buffer salt such as ammonium chloride;
or acid sulfate solutions containing zinc sulfate and a buffer
salt such as aluminum chloride or sulfate. A small concentration
of an organic compound such as glucose, licorice, or glycerin may
be added to the chloride or sulfate baths for brightening
purposes. Formulations for these solutions are given in
References <2) and (3).
In addition to dragout of solution into rinse water which is the
major source of waste, zinc waste is generated during continuous
or batch filtration. Air agitation and hydrogen gas evolution at
cathode surfaces create aerosol particles carried through exhaust
systems into the atmosphere, unless removed by wash water that is
combined with the rinse water for treatment.
Postplating Treatments
Postplating treatment is rare for nickel and chromium- plated
products, but a large portion of zinc-plated steel and a smaller
portion of copper-plated products are processed to impart a
chromate film or one of several alternative colored finishes.
Chemicals utilized for preparing postulating treatment solutions
for copper and zinc electroplates or derived by reactions with
the electroplated metal include the following:
Ammonium carbonate Nickel sulfate
Ammonium hydroxide Nitric acid
Ammonium molybdate Phosphoric acid
Ammonium persulfate Potassium chlorate
Barium sulfide Potassium nitrate
Chromic acid Potassium permanganate
Copper acetate Sodium dichromate
Copper chloride Sodium hydroxide
Copper nitrate Sodium polysulfide
Copper sulfate Sodium sulfide
Ferric chloride sodium thiocyanate
Ferrous sulfate Sulfuric acid
Hydrochloric acid Zinc nitrate
Nickel chloride
45
-------
A dilute solution of nitric acid is an example of a bright dip
bath for zinc plate. A chroma te solution for zinc is always
acidic and contains hexavalent chromium compounds, such as
chromic acid, and contains inorganic and organic compounds as
activators or catalysts known only to the suppliers. Both types
of post-treatment solutions accumulate dissolved zinc and require
dumping and replacement at regular intervals, thereby creating
waste that must be treated prior to discharge. Used chromate-
fi lining solutions also contribute trivalent and hexavalent
chromium ions to wastewater. Water rinsing operations after
bright dipping or chromating also are sources for waste.
Copper (and brass) plated steel and zinc alloy, and zinc-plated
products are sometimes oxidized or otherwise treated in solutions
that produce attractive, desired colors such as those described
in Reference (3) . Some of these solutions are prepared with
copper or other heavy metal salts. Others accumulate dissolved
copper or zinc as a result of use, some of which show up in rinse
water associated with the post treatment. Furthermore, all have
a finite bath life and must be replaced at intervals, like the
bright-dip and chromate-filming solutions used for treating zinc.
Decorative colors are applied on copper and zinc, after
electroplating. Operators frequently develop their own solution
compositions. The following formulation indicate the general
nature of such solutions.
Potassium chlorate, KC1O3 - HO g/1 (5.5 oz/gal)
Nickel sulfate, NL2.SO4.-6H2O - 20 g/1 (2.75 oz/gal)
Copper sulfate, CuSQ4«6H2o - 190 g/1 (24.0 oz/gal)
Li.ght_ brown ..... on:i::cg:|3|3er :
Barium sulfide, BaSJ - 4 g/1 (0.5 oz/gal)
Ammonium carbonate, (NH4) 2CQ3 - 2 g/1 (0.25 oz/gal)
Verde green on copper ;
Copper nitrate, Cu (NQ3) 2 - 30 g/1 (4 oz/gal)
Ammonium chloride, NH4C13 - 30 g/1 (4 oz/gal)
Calcium chloride, CaC12 - 30 g/1 (4 oz/gal)
46
-------
Black^on^zinc:
Ammonium molybdate, NH4MoQ4 - 30 g/1 (4 oz/gal)
Ammonia, NHJ -47 mg/1 (6 fluid oz/gal)
or copper sulfate, CuSQ4*6H2O - 45 g/1 (6 oz/gal)
Potassium chloride, KCl - 45 g/1 (6 oz/gal)
Brown on zinc:
Double nickel salts, (NH4) 2SO4*NiSO4 - 4 g/1 (0.5 oz/gal)
Copper sulfate, CuSO4«6H2O - 4 g/1 (0.5 oz/gal)
Potassium chlorate, KClO_3 - 4 g/1 (0.5 oz/gal)
47
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SECTION VI
SELECTION OFPOLLUTANTPARAMETERS
lntrQd.uctiQn~
This section of the report reviews the waste characterization
detailed in Section V and identifies in terms of chemical,
physical, and biological constituents that which constitutes
pollutants as defined in the act. Rationale for the selection of
wastewater constituents as pollutants is presented.
First, consideration was given to the broad range of chemicals
used in the metal finishing industry. Constituents associated
with the subcategory of electroplating and limited to copper,
nickel, chromium and zinc plating were considered in detail.
Those considered to be potentially toxic pollutants are
identified. Other constituents were examined in the light of
their probable concentration in untreated wastewater in relation
to water quality criteria for discharge, in order to form a
judgment on pollutants to be monitored.
Specific consideration is given in this section to defining the
physical form of metals to be considered pollutants, as well as
definition of analytical techniques for reporting their
concentrations in the wastewater discharge.
A large variety of chemicals used in the metal finishing industry
become wastewater constituents. The important wastewater
constituents for electroplating copper, nickel, chromium, and
zinc were identified in section V. Not all of these constituents
will be found in the wastewaters from every facility since the
number of metals plated in a single facility varies as well as
the number of basic metals pretreated and types of post treatment
operations. Metal finishing operations other than electroplating
and other electroplating operations than copper, nickel,
chromium, and zinc would contribute other metal ions. When
present, these other metal ions are usually coprecipitated with
copper, nickel, chromium, and/or zinc unless they are heavy metal
pollutants of greater potential toxicity requiring special
control and treatment technology. The nonmetallic cations and
anions from electroplating copper, nickel, chromium, and zinc can
be considered typical of the metal finishing industry.
wastewater constituents
The wastewater constituents from electroplating copper, nickel,
chromium, and zinc were identified qualitatively in Section V.
49
Preceding page blank
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Each wastewater constituent is additive to the concentration of
that constituent in the raw water supply if the latter is not
deionized. sometimes constituents in the effluent originate from
the raw water supply.
Table 19 shows approximate quantitative values for a typical
facility plating copper, nickel, chromium, and zinc (Plant 33-1)
with no other metal plating or metal finishing operations other
than electroplating. The values represent the combined raw waste
effluent assuming no treatment and include both chemicals in
wastewater from rinses and concentrated solution dumps collected
and metered uniformly into the wastewater. Good chemical
treatment will oxidize over 99 percent of the cyanide and
normally remove 85 to 99 percent of the metals. The other
constituents in the raw waste having much higher solubilities
than metal hydroxides are usually not removed, and contribute to
the total dissolved solids of the treated effluent.
Some soluble constituents are adsorbed on the insoluble material
and removed during clarification. The concentrations of total
dissolved solids and each soluble constituent depend on the
degree of water conservation used in the facility. The
concentrations shown in Table 19 are considered representative of
the average electroplating facility.
50
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TABLE 19. APPROXIMATE CONCENTRATIONS OF WASTEWATER CONSTITUENTS PRIOR TO
TREATMENT FROM A TYPICAL FACILITY ELECTROPLATING COPPER,
NICKEL, CHROMIUM, AND ZINC (PLANT 33-1)
Estimated Analysis of Water
Untreated Wastewater Treated Effluent Supply
Concentration, Concentration, Analysis,
Wastewater Constituent mg/1 mg/1 mg/1
Copper (Cu+) or Cu2+)
Nickel (Ni+2)
Chromium (Cr-*t)
(Cr6+)
(CrT)
Zinc (Zn2+)
Cyanide (CH~)
Sodium (Na+)
Potassium (K+)
Carbonate (COg )
Orthophosphate (P0^3~)
Pyrophosphate (^2^7 )
Silicate (Si032~)
Metaborate (BO?3")
Perborate (8032-)
Sulfate (S042-)
Bisulfate (11804)
Fluoride (F~)
Fluosilicate (SiF62~)
Tartrate (C4H40s2~)
Chloride (Cl~)
Nitrate (N03~)
Wetting agents (organic)
Sequestrants
Chelates
Additives (organic)
Proprietary acid salts
6.7 0.23
2.4 <0.20
Oi05 0.15
17 <0.05
17 <0.20
32 0.1
50 0.21
465 20
2.4
57
47 3.0 <0.01
53
50
36
1.3
19 20
3.7
0.1 0.1
0.5
8.9
228 25
1.4
6.8
6.5
6.5
0.5
32
Total dissolved solids 1150.
51
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Wastewater Constitugnts §£d Parameters of Pollutional
Significance
The wastewater constituents of pollutional significance for this
segment of the electroplating industry include copper, nickel,
chromium, zinc, cyanide, suspended solids, and pH« It is
recommended that copper, nickel, chromium, zinc, and cyanide be
the subject of effluent limitations and standards of performance
for the electroplating industry regardless of the physical form
(soluble or insoluble metalj or chemical form (e.g., valence
state of metal or type of cyanide complex) . All other metals and
chemical compounds in the wastewater that are not yet
specifically the subject of effluent limitations but which would
normally be precipitated during treatment for removal of copper,
nickel, chromium, and zinc are considered part of the suspended
solids as well as any chemical or biological material adsorbed or
entrapped by the suspended solids during clarification and
separation. Thus, suspended solids are a wastewater constituent
of pollutional significance.
The pH is subject to effluent limitations because it affects the
solubility of metallic compounds such as zinc hydroxide and the
soluble metal content of the treated effluent.
Thus, the major chemical, physical, and biological wastewater
constituents and parameters of pollutional significance are as
follows:
Copper
Nickel
Chromium, hexavalent
Chromium, total
Zinc
Cyanide, amenable to oxidation by chlorine
Cyanide, total
Suspended solids
pH
Other wastewater constituents of secondary importance in the
electroplating industry that are not the subject of effluent
limitations or standards of performance are as follows:
Total dissolved solids
Chemical oxygen demand
Biochemical oxygen demand
oil and grease
Turbidity
Color
Temperature
Rationale for the Selection of wastewater Constituents and
Parameters
52
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Copper salts occur in natural surface waters only in trace
amounts, up to about 0.05 mg/1, so that their presence generally
is the result of pollution.
Copper is not considered to be a cumulative systemic poison for
humans, but it can cause symptoms of gastroenteritis, with nausea
and intestinal irritations, at relatively low dosages. The
limiting factor in domestic water supplies is taste. Threshold
concentrations for taste have been generally reported in the
range of 1.0-2.0 mg/1 of copper, while as much as 5-7,5 mg/1
makes the water completely unpalatable.
The toxicity of copper to aquatic organisms varies significantly,
not only with the species, but also with the physical and
chemical characteristics of the water, including temperature,
hardness, turbidity, and carbon dioxide content. In hard water,
the toxicity of copper salts is reduced by the precipitation of
copper carbonate or other insoluble compounds. The sulfates of
copper and zinc, and of copper and cadmium are synergistic in'
their toxic effect on fish.
Copper concentrations less than 1 mg/1 have been reported to be
toxic, particularly in soft water, to many kinds of fish,
crustaceans, mollusks, insects, phytoplankton and zooplankton.
Concentrations of copper, for example, are detrimental to some
oysters above .1 mg/1. Oysters cultured in sea water containing
0.13-0.5 mg/1 of copper deposited the metal in their bodies and
became unfit as a food substance.
Nickel
Elemental nickel seldom occurs in nature, but nickel compounds
are found in many ores and minerals. As a pure metal it is not a
problem in water pollution because it is not affected by, or
soluble in, water. Many nickel salts, however, are highly
soluble in water.
Nickel is extremely toxic to citrus plants. It is found in many
soils in California, generally in insoluble form, but excessive
acidification of such soil may render it soluble, causing severe
injury to or the death of plants. Many experiments with plants
in solution cultures have shown that nickel at 0.5 to 1.0 mg/1 is
inhibitory to growth.
Nickel salts can kill fish at very low concentrations. Data for
the fathead minnow show death occurring in the range of 5^43
mg/1, depending on the alkalinity of the water.
Nickel is present in coastal and open ocean concentrations in the
range of 0.1 - 6.0 ug/1, although the most common values are 2 -
3 ug/1. Marine animals contain up to 100 ug/1, and marine plants
contain up to 3,000 ug/1. The lethal limit of nickel to some
marine fish has been reported as low as 0.8 mg/1. Concentrations
53
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of 13,1 mg/1 have been reported to cause a 50 percent reduction
of the photo-synthetic activity in the giant kelp fMacrocYS^is
g^rifera) in 96 hours, and a low concentration was found to kill
oyster eggs.
Chromium
Chromium, in its various valence states, is hazardous to man. It
can produce lung tumors when inhaled and induces skin
sensitizations. Large doses of chromates have corrosive effects
on the intestinal tract and can cause inflammation of the
kidneys. Levels of chrornate ions that have no effect on man
appear to be so low as to prohibit determination to date.
The toxicity of chromium salts toward aquatic life varies widely
with the species, temperature, pH, valence of the chromium, and
synergistic or antagonistic effects, especially that of hardness.
Fish are relatively tolerant of chromium salts, but fish food
organisms and other lower forms of aquatic life are extremely
sensitive. Chromium also inhibits the growth of algae.
In some agricultural crops, chromium can cause reduced growth or
death of the crop. Adverse effects of low concentrations of
chromium on corn, tobacco and sugar beets have been documented.
Hexavalent chromium is considered to be most active of the
chromium species. Hexavalent chrome also is an indicator of the
effectiveness of a. chemical step to control total chromium.
zinc
Occurring abundantly in rocks and ores, zinc is readily refined
into a stable pure metal and is used extensively for galvanizing,
in alloys, for electrical purposes, in printing plates, for dye-
manufacture and for dyeing processes, and for many other
industrial purposes. Zinc salts are used in paint pigments,
cosmetics, Pharmaceuticals, dyes, insecticides, and other
products too numerous to list herein. Many of these salts (e.g.,
zinc chloride and zinc sulfate) are highly soluble in water;
hence it is to be expected that zinc might occur in many
industrial wastes. On the other hand, some zinc salts (zinc
carbonate, zinc oxide, zinc sulfide) are insoluble in water and
consequently it is to be expected that some zinc will precipitate
and be removed readily in most natural waters.
In zinc-mining areas, mine has been found in waters in
concentrations as high as 50 mg/1 and in effluents from metal-
plating works and small-arms ammunition plants it may occur in
significant concentrations. In most surface and ground waters,
it is present only in trace amounts. There is some evidence that
zinc ions are adsorbed strongly and permanently on silt,
resulting in inactivation of the zinc.
54
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Concentrations of zinc in excess of 5 mg/1 in raw water used for
drinking water supplies cause an undesirable taste which persists
through conventional treatment. Zinc can have an adverse effect
on man and animals at high concentrations.
In soft water, concentrations of zinc ranging from 0.1 to 1.0
mg/1 have been reported to be lethal to fish. Zinc is thought to
exert its toxic action by forming insoluble compounds with the
mucous that covers the gills, by damage to the gill epithelium,
or possibly by acting as an internal poison. The sensitivity of
fish to zinc varies with species, age and condition, as well as
with the physical and chemical characteristics of the water.
Some acclimatization to the presence of zinc is possible. It has
also been observed that the effects of zinc poisoning may not
become apparent immediately, so that fish removed from zinc-
contaminated to zinc-free water (after 4-6 hours of exposure to
zinc) may die 48 hours later. The presence of copper in water
may increase the toxicity of zinc to aquatic organisms, but the
presence of calcium or hardness may decrease the relative
toxicity.
Observed values for the distribution of zinc in ocean waters vary
widely. The major concern with zinc compounds in marine waters
is not one of acute toxicity, but rather of the long-term sub-
lethal effects of the metallic compounds and complexes. From an
acute toxicity point of view, invertebrate marine animals seem to
be the most sensitive organisms tested. The growth of the sea
urchin, for example, has been retarded by as little as 30 ug/1 of
zinc.
Zinc sulfate has also been found to be lethal to many plants, and
it could impair agricultural uses.
Cy_anide
Cyanides in water derive their toxicity primarily from
undissolved hydrogen cyanide (HCN) rather than from the cyanide
ion (CN-). HCN dissociates in water into H* and CN~ in a pH-
dependent reaction. At a pH of 7 or below, less than 1 percent
of the cyanide is present as CN~; at a pH of 8, 6,7 percent; at a
pH of 9, 42 percent; and at a pH of 10, 87 percent of the cyanide
is dissociated. The toxicity of cyanides is also increased by
increases in temperature and reductions in oxygen tensions. A
temperature rise of 10°C produced a two- to threefold increase in
the rate of the lethal action of cyanide.
Cyanide has been shown to be poisonous to humans, and amounts
over 18 mg/1 can have adverse effects, A single dose of 50-60 mg
is reported to be fatal.
Trout and other aquatic organisms are extremely sensitive to
cyanide. Amounts as small as .1 mg/1 can kill them. Certain
metals, such as nickel, may complex with cyanide to reduce
lethality especially at higher pH values, but zinc and cadmium
cyanide complexes are exceedingly toxic.
55
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When fish are poisoned by cyanide, the gills become considerably
brighter in color than those of normal fish, owing to the
inhibition by cyanide of the oxidase responsible for oxygen
transfer from the blood to the tissues.
Ic-tal Suspended solids
Suspended solids include both organic and inorganic materials.
The inorganic components include sand, silt, and clay. The
organic fraction includes such materials as grease, oil, tar,
animal and vegetable fats, various fibers, sawdust, hair, and
various materials from sewers. These solids may settle out
rapidly and bottom deposits are often a mixture of both organic
and inorganic solids. They adversely affect fisheries by
covering the bottom of the stream or lake with a blanket of
material that destroys the fish-food bottom fauna or the spawning
ground of fish. Deposits containing organic materials may
deplete bottom oxygen supplies and produce hydrogen sulfide,
carbon dioxide, methane, and other noxious gases.
In raw water sources for domestic use, state and regional
agencies generally specify that suspended solids in streams shall
not be present in sufficient concentration to be objectionable or
to interfere with normal treatment processes. Suspended solids
in water may interfere with many industrial processes, and cause
foaming in boilers, or encrustations on equipment exposed to
water, especially as the temperature rises. Suspended solids are
undesirable in water for textile industries; paper and pulp;
beverages; dairy products; laundries; dyeing; photography;
cooling systems, and power plants. Suspended particles also
serve as a transport mechanism for pesticides and other
substances which are readily adsorbed onto clay particles.
Solids may be suspended in water for a time, and then settle to
the bed of the stream or lake. These settleable , solids
discharged with manfs wastes may be inert, slowly biodegradable
materials, or rapidly decomposaole substances. While in
suspension, they increase the turbidity of the water, reduce
light penetration and impair the photosynthetic activity of
aquatic plants.
Solids in suspension are aesthetically displeasing. when they
settle to form sludge deposits on the stream or lake bed, they
are often much more damaging to the life in water, and they
retain the capacity to displease the senses. Solids, when
transformed to sludge deposits, may do a variety of damaging
things, including blanketing the stream or lake bed and thereby
destroying the living spaces for those benthic organisms that
would otherwise occupy the habitat. When of an organic and
therefore decomposable nature, solids use a portion or all of the
dissolved oxygen available in the area. Organic materials also
serve as a seemingly inexhaustible food source for sludgeworms
and associated organisms.
56
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Turbidity is principally a measure of the light absorbing
properties of suspended solids. It is frequently used as a
substitute method of quickly estimating the total suspended
solids when the concentration is relatively low.
gH, Acidity and Alkalinity
Acidity and alkalinity are reciprocal terms. Acidity is produced
by substances that yield hydrogen ions upon hydrolysis and
alkalinity is produced by substances that yield hydroxyl ions.
The terms "total acidity" and "total alkalinity" are often used
to express the buffering capacity of a solution. Acidity in
natural waters is caused by carbon dioxide, mineral acids, weakly
dissociated acids, and the salts of strong acids and weak bases.
Alkalinity is caused by strong bases and the salts of strong
alkalies and weak acids.
The term pH is a logarithmic expression qf the concentration of
hydrogen ions. At a pH of 7, the hydrogen and hydroxyl ion
concentrations are essentially equal and the water is neutral.
Lower pH values indicate acidity while higher values indicate
alkalinity. The relationship between pH and acidity or
alkalinity is not necessarily linear or direct,
waters with a pH below 6,0 .are- corrosive to water .wprHs
structures, distribution lines, and household plviHibing fixtusces;
and can thus add such constituents to drinking water as iron>
copper, zinc, cadmium and lead. The hydrogen ion concfnt-jratioil
can affect the "taste" of the water. At a low pH water tastes.
"sour". The bactericidal effect of chlorine is weakened as the
pH increases, and it is advantageous to keep the pH close to 7.
This is very significant for providing safe drinking water,
Extremes of pH or rapid pH changes can exert stress conditions or
kill aquatic life outright. Dead fish, associated algal blooms,
and foul stenches are aesthetic liabilities of any waterway.
Even moderate changes from "acceptable" criteria limits of pH are
deleterious to some species. The relative toxicity to aquatic
life of many materials is increased by changes in the water pH.
Metalocyanide complexes can increase a thousand-fold in taxieity
with a drop of 1,5 pH units. The availability of many nutrient
substances varies with the alkalinity and acidity. Ammonia is
more lethal with a higher pH. ,
The lacrimal fluid of the human eye has a pH of approximately 7,0
and a deviation of 0.1 pH unit from the norm may result in eye
irritation for the swimmer. Appreciable irritation will cause
severe pain.
Ratigna1e_fgrrR§1get ion of_Qther
W§ gtewat gr __ Cons tit ue ntsn a s_ Pgllut.ants
Metals
5?
-------
The rationale for rejection of any metal other than copper,
nickel, chromium, and zinc as a pollutant is based on one or more
of the following reasons:
(1) They would not be expected to be present in
electroplating wastes from copper, nickel,
chromium, and zinc plating processed in
significant amounts
-------
effluent, with electroplating wastes prior to "treatment, BOD would
be considered a major parameter.
Oil and Grease
Oil and greaise is not normally a significant pollution parameter
in the electroplating industry because these materials are
removed from workpieees by nonaqueous solvents. Added pollution
reduction is usually achieved by the usual practice of installing
oil and grease skimmers on settling tanks. Where such control
practices are absent, oil and grease might be considered a
parameter subject to control and measurement.
Turbidity
Turbidity is indirectly measured and controlled independently by
the limitation on suspended solids.
Color
color is not usually significant in wastewater from
electroplating and is indirectly controlled by the effluent
limitations on suspended solids and on total metal which controls
the amount of colloidal metal that could color the effluent.
Temperature
Temperature is not considered a significant pollution parameter
in the electroplating industry. However, cooling water used to
cool plating process tanks and/or evaporative recovery systems
that are not subsequently used for rinsing could contain
pollutants from leaks in the system; Insufficient data exists
upon which to base effluent limitations and standards of
performance.
59
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SECTION VII
COimgOL^AND^TREATMENT^TECgNOLQgY
Introduc t ion
The control and -treatment technology for reducing the discharge
of pollutants from copper, nickel, chromium, and zinc
electroplating processes is discussed in this section.
control of electroplating wastewaters includes process
modifications, material substitutions, good housekeeping
practices, and water conservation techniques. The in-plant
control techniques discussed are generally considered to be
normal practice in this industry.
The treatment of electroplating wastewaters includes all
techniques for the removal of pollutants and all techniques for
the concentration of pollutants in the wastewaters for subsequent
removal by treatment. Although all of the treatment technologies
discussed have been applied to electroplating wastewaters, some
may not be considered normal practice in this industry.
Chemical treatment technology is discussed first in this section
because treatment of all waste water generated by electroplating
is required, prior to water discharge into navigable streams,
irrespective of the in-plant controls adopted for reducing waste.
Nevertheless, it is emphasized that the amount of pollutants
discharged to navigable waters is directly proportional to the
volume of water discharged,
The proper design, operation, and maintenance of all wastewater
control and treatment systems are considered essential to an
effective waste management program. The choice of an optimum
wastewater control and treatment strategy for a particular
electroplating facility requires an awareness of numerous factors
affecting both the quantity of wastewater produced and its
amenability to treatment.
Chemical^Treatment Technology
Applicability
Chemical treatment processes for waste water from electroplating
operations are based on chemical reactions utilized for 25 years
or more. A system has evolved that is capable of effectively
treating effluents from plants of any size and reducing metal ion
concentrations in the effluent to 0.5 mg/liter or less. Control
procedures have been devised to maintain the effectiveness of the
process under a variety of operating conditions.
Processes
Preceding page blank
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Separation,, of Streams. The rinse waters are usually segregated
into three streams prior to treatment, and consist of 1) those
containing Cr+6, 2) those containing cyanide, and 3) the
remainder, constituting water from acid dips, alkali cleaners,
acid copper, nickel, and zinc baths, etc. The cyanide is
oxidized by chlorine and Cr+6 is reduced to Cr+3 with sulfur
dioxide or other reducing agents. The three streams are then
combined and the metal hydroxides are precipitated by adjustment
of the pH. The hydroxides are allowed to settle out, often with
the help of coagulating agents, and the sludge is hauled to a
lagoon or filtered and used as land fill. The treatment
facilities may be engineered for batch, continuous, or integrated
operation (7).
Batch^Treatment. The batch method is generally used for small or
medium-sized plants. Batch treatment is useful not only for
rinse waters but for process solutions containing high
concentrations of chemicals such as floor spills. Holding tanks
collect the wastewater and are large enough to provide ample time
to treat, test, and drain a tank while another is being filled.
Analytical tests are made before treatment to determine the
amount of reagent to add and after treatment to establish that
the desired effluent concentrations have been obtained.
SQntinuous_Treat.|nent» The chemical treatment process may be made
continuous by (1) sizing and baffling treatment tanks to provide
sufficient hold times to complete chemical reactions; (2)
providing continuous monitoring of pH and oxidation/reduction
potentials and controls for regulating reagent additions by means
of these monitors; and (3) providing a continuous-overflow
settling tank that allows sludge to be pumped off periodically
through the bottom.
A. diagram of a continuous-treatment plant operating at maximum
capacity is shown in Figure 4. The dilute acid-alkali stream
originates from rinses associated with alkaline cleaners, acid
dips, and baths containing metal ions but no cyanide or
hexavalent chromium. When concentrated acid and alkali baths are
to be discarded they are transferred to a holding tank and added
slowly to the dilute stream. In this manner, sudden demands on
the reagent additions and upsetting of the treatment conditions
are avoided. The dilute acid-alkali stream first enters a surge
tank to neutralize the wastewater and equalize the composition
entering the precipitation tank. The hexavalent chromium is
reduced at a pH of 3.5, and the addition of the SO2 and HC1 are
controlled by suitable monitors immersed in the well-agitated
reduction tank. Cyanide is destroyed in a large tank with
compartments to allow a two-stage reaction. Reaction time is
about 3 hours.
The treated chrome, cyanide, and neutralized acid- alkali streams
are run into a common tank where pH is automatically adjusted to
and held at 8.8. The stream then enters a solids contact unit
where mixing, coagulation, flocculation, recirculation, solid
separation, clarification, solids concentration, sludge
62
-------
CTi
(/J
.atronn.
Final
Neutral""
ization S
Precipita-
tion
strong
cyanide
veak
hold
J46 ^
4
1
350
cyanide gpm **~ gpa
v y
Y
Destruc-
tion
350
1
1300
f
Ifier
t '
i
— »*»•
L?e
Filter
1
i
•«
gpm
1.8 gpn
Bl'Jdge
FIGURE 4. DIAGRAM OF A TYPICAL CONTINUOUS-TREATMENT PLANT
-------
collection, and sludge removal are accomplished. Floceulants are
continuously added to this tank. Typically, residence time is 2
hours. The effluent from this tank constitutes the discharge
from the plant.
Integrated ^Treatment. The integrated system uses a reservoir
tank in conjunction with the rinse tanks for each type of plating
bath. A common solution is circulated through the chemical wash
tank {which replaces what is normally the first rinse tank) and
the reservoir. The solution contains an excess of treatment
chemical so that cyanide destruction takes place in the wash tank
and directly on the film of drag-out solution on the part itself.
Therefore, no cyanide is dragged into the subsequent rinse tank
and no treatment is required for effluent from this tank. Metal
hydroxides settle in the reservoir and may be recovered,
dissolved, and returned to the plating bath from which they
originated. In contrast to batch and continuous treatments,
which are generally carried out in a separate facility, the
reservoir in the integrated system is in proximity to the plating
room because of the necessity for circulation. The layout of an
integrated system for treating rinse water waste from a cyanide
plating solution and a chromium plating bath is shown in Figure
5.
64
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Reuse WATCH
rh
U1
too run
HYfOCHLOTITt
I 1
CYANIDE WASTE
TfltATHCNT RCteflVOIK
£
$
u
b-
t
CHROWIUM WA
TREATMENT R!
S
Jl .,
TO
CLARIflEU
WATER REUSE PUMP
WATtft BLOW DOWN
TO SCWEK
SODIUM CAMBQHATK
OOOIUU HVOKO-
•UtflTI
•TO »LUO»C KB
FIGURS 5. INTEGRATED TREATMENT SYSTEM
-------
Unit Operations
Preg4gitation. The effluent levels of metal ions attainable by
chemical treatment depend upon the insolubility of metal
hydroxides in the treated water and upon the ability to
mechanically separate the hydroxides from the process stream.
Minimum solubility is attained at a pH in the range of 6 to 9
depending upon the specific conditions present. Effects of
coprecipitation and adsorption on the flocculating agents added
to aid in settling the precipitate play a significant role in
reducing the concentration of the metal ions. Dissolved solids
made up of noneommon ions can increase the solubility of the
metal hydroxides according to the Debye- Huckel Theory. In a
treated solution from a typical electroplating plant, which
contained 230 mg/1 of sodium sulfate and 1060 mg/1 of sodium
chloride, the concentration of nickel was 1.63 times its
theoretical solubility in pure water. Therefore, salt
concentrations up to approximately 1000 ppm should not increase
the solubility more than 100 percent as compared to the
solubility in pure water. However, dissolved solids
concentrations of several thousand ppm could have a marked effect
upon the solubility of the hydroxide.
When solubilizing complexing agents are present, the equilibrium
constant of the complexing reaction has to be taken into account
in determining theoretical solubility with the result that the
solubility of the metal is generally increased. Cyanide ions
must be destroyed not only because they are toxic but also
because they prevent effective precipitation of copper and zinc
as hydroxides. If cyanide is replaced in a plating bath by a
nontoxic complexing agent such as IOTA (ethylene-diamine-
tetraacetic acid), the new complexing agent could have serious
consequences upon the removal of metal ions by precipitation.
Solids.,,Separation. The first step in separating the precipitated
metals is settling, which is very slow for gel- like zinc
hydroxide, but accelerated by coprecipitation with the hydroxides
of copper and chromium (10). Coagulation can also be aided by
adding metal ions such as ferric iron which forms ferric
hydroxide and absorbs some of the other hydroxide, forming a
floe. Ferric iron and aluminum sulfate have been used for this
purpose in sewage treatment for many years. Ferric chloride is
frequently added to the clarifier of chemical waste—treatment
plants in plating installations, Flocculation and settling are
further improved by use of polyelectrolytes, which are high
molecular weight polymers containing several ionizable ions. Due
to their ionic character they are capable of swelling in water
and adsorbing the metal hydroxide which they carry down during
settling.
Settling is accomplished in the batch process in a stagnant tank,
and after a time the sludge may be emptied through the bottom and
the clear effluent drawn off through the side or top. The
continuous system uses a baffled tank such that the stream flows
66
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first to the bottom but rises with a decreasing vertical velocity
until the floe can settle in a practically stagnant fluid.
Clarifiers are widely used throughout the industry to attain more
efficient solids removal. Polishing filters or sand filters may
be used on the effluent following clarification to achieve even
greater removal.
Sludge ..._Qispgsa4« Clarifier underflow or "sludge" contains
typically 1 to 2 percent solids and can be carried to a lagoon.
Run-off through porous soil to ground-water is objectionable
since precipitated metal hydroxides tend to get into adjacent
streams or lakes. Impervious lagoons require evaporation into
the atmosphere. However, the average annual rainfall balances
atmospheric evaporation. Additionally, heavy rainfalls can fill
and overflow the lacfoon. Lagooning can be avoided by dewatering
the sludge to a semidry or dry condition.
Several devices are available for dewatering sludge. Rotary
vacuum filters will concentrate sludge containing H to 8 percent
solids to 20 to 25 percent solids. Since the effluent
concentration of solids is generally less than 4 percent a
thickening tank is generally employed between the clarifier and
the filter. The filtrate will contain more than the allowed
amount of suspended solids, and must, therefore, be sent back to
the clarifier.
Centrifuges will also thicken sludges to the above range of
consistency and have the advantage of using less floor space.
The effluent contains at least 10 percent solids and is returned
to the clarifier.
Pressure filters may be used. In contrast to rotary filters and
centrifuges, pressure filters will produce a filtrate with less
than 3 mg/1 of suspended solids so that return to the clarifier
is not needed. The filter cake contains approximately 20 to 25
percent solids. Pressure filters are usually designed for a
filtration rate of 2.01 to 2.H liters/min/sq m (0.05 to 0.06
gpm/sq ft) of clarifier sludge.
Solids contents from 25 to 35 percent in filter cakes can be
achieved with semi-continuous tank filters rated at 10.19 to
13.11 liters/min/sq m (0.25 to 0.33 gpm/sq ft) surface. A solids
content of less than 3 mg/1 is normally accepted for direct
effluent discharge. The units require minimum floor space.
Plate and frame presses produce filter cakes with 10 to 50
percent dry solids and a filtrate with less than 5 mg/1 total
suspended solids. Because automation of these presses is
difficult, labor costs tend to be high. The operating costs are
partially off-set by low capital equipment costs.
Automated tank type pressure filters are just now finding
application. The solids content of the cake can be as high as 60
67
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percent while the filtrate may have up to 5 mg/1 of total
suspended solids. The filtration rate is approximately 2.04
liters/min/sq m (0.05 gpm/sq ft) filter surface area. Pressure
filters can also be used directly for neutralized wastes
containing from 300 to 500 mg/1 suspended solids at design rates
of 4.88 to 6.52 liters/min/sq m (0.12 to 0.16 gpm/sq ft) and
still maintain a low solids content in the filtrate.
Filter cakes can easily be collected in solid waste containers
and hauled away to land fills. There may be situations, however,
where the metal in the filter cake could redissolve if it came
into contact with acidic water. Careful consideration should be
given to where such a material is dumped.
Several companies have developed proprietary chemical fixation
processes which are being used to solidify sludges prior to land
disposal. In contrast to filtration, the amount of dried sludge
to be hauled away is increased. Claims are that the process
produces insoluble metal ions so that in leaching tests only a
fraction of a part per million is found in solution. However,
much information is lacking on the long term behavior of the
"fixed" product, and potential leachate problems which might
arise. The leachate test data and historical information to date
indicate that the process has been successfully applied in the
disposal of polyvalent metal ions and it apparently does have
advantages in producing easier to handle materials and in
eliminating free water. Utilization of the chemical fixation
process is felt to be an improvement over many of the
environmentally unacceptable disposal methods now in commong
usage by industry. Nevertheless, chemically fixed wastes should
be regarded as easier to handle equivalents of the raw wastes and
the same precautions and requirements required for proper
landfilling of raw waste sludges should be applied.
The possibility of recovering metal values from sludges
containing copper, nickel, chrome, and zinc has been consid-
ered (12) but such a system appears to be uneconomic under present
circumstances. It may be profitable to recover metal values if
900 to 2300 kg (2,000 to 5,000 pounds) of dried sludge solids can
be processed per day with a thoroughly developed process. To
attain this capacity would almost certainly require that sludge
from a large number of plants be brought to a central processing
station. The recovery would be simpler if the metallic
precipitates were segregated, but segregation would require
extensive modifications, investment, and increased operating
expense for precipitation and clarification. Laboratory
experiments showed that zinc could be leached from sludge with
caustic after which copper, nickel, and chromium were effectively
dissolved with mineral acids. Ammonium carbonate dissolved
copper and nickel but not trivalent chromium, thus giving a
method of separation. Eleetrowinning of the nickel and copper
appeared to be a feasible method of recovering these metals.
-------
Oper at ing Sy it ems;. Relatively few plating installa-
tions have installed filters, although the problems of disposing
of unfiltered sludge should provide an impetus for use of more
filters in the future. Plant 12-8 has a large rotary filter in
routine operation, " and the practicality of this unit has been
well established. The Chemfix system is in use at several
plants.
DemonstrationStatus. centrifuges are used for dewatering sludge
in the new waste treatment facility at Rock Island Arsenal.
Since the whole waste treatment system at Rock Island has not yet
been operated on a continuous basis the feasibility of the
concepts and the components used remains to be demonstrated.
cyan ide^ Oxidation. Cyanide in wastewaters is commonly destroyed
by oxidation with chlorine or hypochlorite prior to precipitation
of the metal hydroxides. The method is simple, effective, and
economically feasible even for small volume installations. A
comprehensive study of the method was made by Dodge and
Zabban(10-13), the results of which have been used to work out
the practical processes. The following are proposed reactions
for chlorine oxidation:
(1) NaCN + C12 -+CNC1 + NaCl
(2) CNC1 + 2NaOH —*NaCNO + NaCl + H2O
(3) 2NaCNO + 3C12 + t»NaOH —*N2 + 2CQ2 * 6NaCl + 2B20.
Reaction (2) goes rapidly at pH 11.5, under which conditions,
build up of the toxic gas CNCl by Reaction (1) is avoided.
Treatment of dilute rather than concentrated solutions also
minimizes its formation. Oxidation to cyanate (NaCNO) is
completed in 5 minutes or less. Reaction (3) goes more slowly,
requiring an hour in the preferred pH range of 7.5 to 9.0, and a
longer time at higher pH. After the conversion to nitrogen and
carbon dioxide, excess chlorine is destroyed with sulfite or
thiosulfate.
Sodium hypochlorite may be used in place of chlorine. Recent
technical innovations in electrochemical hypochlorite generators
for on-site use raise the possibility of controlling the addition
of hypochlorite to the cyanide solution by controlling the
current to the electrochemical generator, using sodium chloride
as the feed material.
Concentrated solutions, such as contaminated or spent baths,
cyanide dips, stripping solutions, and highly concentrated
rinses, are normally fed at a slow rate into a dilute cyanide
stream and treated with chlorine. However, concentrated
solutions may also be destroyed by electrolysis with conventional
equipment available in the plating shop (18). In normal
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industrial practice the process is operated batchwise, whereas
the optimum system, from an operating standpoint, would be a
cascaded one in which successively larger tanks are operated at
successively lower current densities. This is the more efficient
system. In addition to the oxidation of cyanide at the anode,
valuable metal can be recovered at the cathode. The process
becomes very inefficient when the cyanide concentration reaches
10 ppm, but at this point the solution can be fed into the
process stream for chemical destruction of cyanide to bring the
concentration to the desired level. The addition of chloride
ions to the concentrated solutions, followed by electrolysis,
produces chlorine or hypochlorite in solution, which can then
destroy the cyanide to the same low levels as obtained by direct
chlorination. With the provision that chlorine or hypochlorite
be formed at a rate equal to the concentration of cyanide passing
through the system, the process can be operated continuously:
2NaCN + 2NaOCl—-» 2NaCNO + 2NaCl
2NaCNO3 + 3NaOCl -I- H20 —*• 2C02 + N2 +2NaOH + 3NaCl
2NaCN + SNaOCl + H2O —-* 2C02 + N2 + 2NaOH + SNaCl.
One proprietary process (A), based on the above principles,
claims to produce 1 kg of active chlorine per 5,5 KwH (19)»
Equipment needs are the same with the exception that the tanks
must be lined and graphite or platimized anodes must be used.
Polysulfide-cyanide strip solutions containing copper and nickel
do not decompose as readily and as completely as do plating
solutions. Although the cyanide content can be reduced from
75,000 to 1000 rng/1 during two weeks of electrolysis anode
scaling prevents further cyanide decomposition unless anodes are
replaced or freed from scale. Minimum cyanide concentration
attainable is about 10 mg/1 after which the solution can be
treated chemically.
The electrolysis of dilute cyanide solution can be improved by
increasing the electrode area. Area can be increased by filling
the space between flat electrodes with carbonaceous particles
(20). The carbon particles accelerate the destruction process
1000 times, but flow rate through the unit must be carefully
adjusted, if used on a continuous basis to achieve complete
destruction (Plant 30-1).
Although cyanide can be destroyed by oxygen or air under suitable
conditions (21,22)r cyanide concentrations in the effluent are
reported to be 1,3 to 2.2 mg/1, which is high for discharge to
sewers or streams. A catalytic oxidation unit using copper
cyanide as a catalyst and activated carbon as the reactive
surface has been described for oxidizing cyanide with air or
oxygen(23), and at least two units were put in operation. The
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most recent information on these units is that they are not
operating and that at present the units are not being sold.
Ozone will oxidize cyanide (to cyanate) to below detectable
limits independent of the starting concentration or of the
complex form of the cyanide (2*1,25,26) . The reaction can be
completed even with the very stable iron complexes if heat or
ultraviolet light is used in conjunction with the ozone. The
potential advantages of ozone oxidation are enhanced by the
efficiency and reliability of modern ozone .generators, and
development work is continuing.
A method employing thermal decomposition for cyanide destruction
has been recently announced (27). Cyanide solution is heated to
160 to 200 C under pressure for 5 to 10 minutes. Ammonia and
formate salts are formed. No information is given on the final
cyanide concentration.
Another proprietary process (B) claims to destroy cyanides of
sodium, potassium, zinc, and cadmium and also precipitates zinc
and cadmium. The process is discussed later in this section.
Precipitation of cyanide as ferrocyanide is restricted to
concentrated wastes. Ferrocyanide is less toxic than cyanide,
but is converted back to cyanide in sunlight. Treatment is
accomplished by adding an amount in excess of stoichiometry (2.3
kg of FeSO4 per kg of cyanide). Large amounts of sludge are
produced which add to the pollution load. Complex cyanides do
not break down readily and the reaction stops when a
concentration of 10 mg/1 of cyanide is reached. No benefits can
be foreseen in terms of reducing waste volume and concentration.
Cyanide is also destroyed by reaction with polysulfides.
Reasonable reaction rates are obtained only if the solution is
boiled. Since the reaction does not destroy all of the cyanide
further treatment is necessary.
For a small electroplating facility, it is conceivable that an
electrodialysis system for the distruction of cyanide could be
installed. Experimental work has been performed on copper
cyanide plating baths and is applicable to cyanide baths of zinc,
cadmium, silver, and gold.
Reduction of Hexayalent.^Chromium. Hexavalent chromium (Cr+6) is
usually reduced to trivalent chromium at a pH of 2 to 3 with
sulfur dioxide (SO2), sodium bisulfite, other sulfite-containing
compounds, or ferrous sulfate. The reduction makes possible the
removal of chromium as the trivalent hydroxide which precipitates
under alkaline conditions. Typical reactions for SO2 reduction
are as follows:
SO2 + H2O —* H,2SO3
2H2CO4 + 3H2SO3—-*Cr2 (SO4) 3 + 5H2O.
71
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Representative reactions for reduction of hexavalent chromium
under acidic conditions using sulfite chemicals instead of S02_
are shown be lows
(a) Using sodium metabisulfite with sulfuric acid:
4H2CrO£ + 3Na2S20!5 + 3H2SO£ - - *3Na2SO£ + 2Cr_2 (SO 4) 3_ + 7H20
(b) Using sodium bisulfite with sulfuric acid:
4H2CrO£ + 6NaHS03_ + 3H2SO_4— *3Na2S04_ + 2er2_(SO£}3 + lOH^O
(c) Using sodium sulfite with sulfuric acid:
2H2CrO + 3Na2S03 + 3H2SO — +3NaSQ + Cr2SO)3 + 5H2Q.
Reduction using sulfur dioxide is the most widely used method,
especially with larger installations. The overall reduction is
readily controlled by automatic pH and ORP (oxidation-reduction
potential) instruments. Treatment can be carried out on either a
continuous or batch basis.
Hexavalent chromium can also be reduced to' trivalent chromium in
an alkaline environment using sodium hydrosulfite as follows:
2H2_CrO£ + 3N2H2_ Na2CO3 2Cr(OH)3_ + 3N2_ +2H20.
As indicated in the above equation, the chromium is both reduced
and precipitated in this one-step operation. Results similar to
those obtained with sodium hydrosulfite can be achieved using
hydrazine under alkaline conditions.
2H2CrO£ + 3N2H2_ Na2C03 2Cr(OH)3
2H20.
Sodium hydrosulfite or hydrazine are frequently employed in the
precipitation step of the integrated system to insure the
complete reduction of any hexavalent chromium that might have
been brought over from the prior reduction step employing sulfur
dioxide or sodium bisulfite. Where ferrous sulfate is readily
available (e.g., from steel pickling operations), it can be used
for reduction of hexavalent chromium j the reaction is as follows:
2CrO3 + 6FeSO4*7H2O + 6H2SQ
Cr2(SO43 + 13H20.
,Cr+6 may be reduced at a pH as high as 8.5 with a proprietary
compound (28) . It is not necessary to segregate chromate-
containing wastewaters from the acid-alkali stream, and the use
of acid to lower pH is eliminated in this case. Precipitation of
chromic hydroxide occurs simultaneously in this case with the
reduction.
72
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chromic hydroxide occurs simultaneously in this case with the
reduction.
Cr*6 ions may be reduced electrochemically.(26) concentration of
100 rag/1 was reduced to less than 1 mg/1 with a power consumption
of 1.2 kwh/1,000 liters. The carbon bed electrolytic process
previously described for cyanide(2^) may also be used for
chromate reduction in acid solution and Plant 30-1 has achieved a
Cr+6 concentration of .01 mg/1 using this method. Electrolysis
may also be used to regenerate a reducing agent. A process(27)
has been described involving the reduction of Fe(III) to Fe(II)
electrochemically and the reduction of Cr+5 by Fe(II). The
method should be capable of achieving low Cr** levels.
The simultaneous reduction of Cr*6 and oxidative destruction of
cyanide finds limited application in waste-treatment practice.
The reaction requires mixing of Cr*6 and CN in ratios between 2
and 3 using Cu*z as a catalyst in concentrations of 50 to 100
mg/1. The catalyst introduces additional pollutant into the
waste stream. Reaction rates are generally slow, requiring from
6 to 2H hours for cyanide concentrations ranging from 2,000 to
less than 50 mg/1 at a solution pH of 5. The slowness of the
reaction and the high initial concentrations of reactants
required may make the method unsuitable for treating rinse
waters. Its use is limited to batch treatment of concentrated
solutions. No benefits are obtained in terms of water volume and
pollution reduction. Destruction is not as complete as obtained
by the more common chemical methods.
Practical Operating Systems
Chemical treatment is used by every plant contacted during the
effluent guidelines study with the exception of those that are
allowed to discharge plating waste effluents into sewers or
streams without treatment.
The effectiveness of chemical treatment techniques depends on the
nature of the pollutant, the nature and concentration of
interfering ions, the procedure of adding the appropriate amount
of chemicals (or adjusting pH), the reaction time and temperature
and the achievement of effective separation of precipitated
solids. The concentration of an individual pollutant in the
solution being treated has no effect on its final concentration
after treatment. On the other hand, effective removal of heavy
metal pollutants is inhibited by some types of chelating ions
such as tartrate or ethylene diamine tetracetate ions.
The concentrations of metals and cyanide achievable by the
chemical techniques employed for treating waste from copper,
nickel, chromium, and zinc electroplating and zinc chromating
processes are summarized in Table 20. Concentrations lower than
those listed as maximum in Table 20 were reported by companies
using all three (continuous, batch, and integrated) treating
systems. The data show that the soluble concentration levels
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TASK 20 CONCENTRATIONS OF HEAVY METALS AS0 CTAHI15E ACHEVABLE BY
CKEMICAI, TRlAtMB OF WASTE CREATED BIT COPPER, RICKEL,
ASO ZIHC PLAXI8G AND ZIHC CHROKftTISG OPERATIONS
Soluble Cgncentratton After Chemical Treating Contribution Prom Suspended '
Pollutant Minimum, mg/l Maximum, mg/ii 1) Minimum, ng/j8 Maximum,
Cyanide, oxidlzable^3)
Cyanide, total
Phosphorus
Chromium "*
Chromium, total
Copper
Nickel
Zinc
< 0.01
0.1
0.007
< 0.01
0.05
< 0.01
< 0.01
0.05
0.03
0.2
0.6
0.05
0.25
0.2
0.5
0.5
__
—
__
__
0.02
0.02
O.OZ
0.04
,,
—
._
__
0.30
0.76
0.15
0.80
Total suspended solids^ ' 20. 24.
(1) Values below these limits have been reported by plants utilizing continuous (Plants 40-6, 8-4, 33-6, and 11-8),
batch (Plants 36-1, 21-3, and 33-3} and integrated (Plants 36-2 and 20-13} treatment techniques. Others
(Plants 3-3 and 33-3) utilize a combination of integrated and batch or continuous treatments to achieve these
or lower limits.
(2) Data for Plants 33-1, 12-8, 36-1 and 11-8 .
(3) Oxidtzable by chlorine.
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achieved in practice are near those that would be expected based
on solubility data discussed previously.
Higher-than-normal concentrations of copper, nickel, chromium,
and zinc, when they occur, are usually caused by: (1) inaccurate
pH adjustment (sometimes due to faulty instrument calibration);
(2) insufficient reaction time: or (3) excessive concentrations
of chelating agents that complex the metal ions and prevent their
reaction with hydroxyl ions to form the insoluble metal hydrates.
The causes for higher-than-normal concentrations of cyanide are
similar, but another important factor must be added to the list
of potential causes for incomplete cyanide destruction. In this
case, sodium hydroxide and chlorine must be added and provide
sufficient reagent to complete the reaction, which is normally
monitored by an oxidation-reduction-potential (ORP) recorder-
controller. The maintenance of this system is a critical factor
affecting the effectiveness of chemical oxidation.
suspended _Sol j.ds. The suspended solids discharged after
treatment and clarification sometimes contribute more copper,
chromium, and zinc than the soluble metal concentrations, as
shown in Table 20. For example, the copper contribution from the
total suspended solids determined for four plants engaged in
copper, nickel, chromium, and zinc electroplating was in the
range of 0.02 to 0,76 mg/1. Zinc contributions from suspended
solids ranged from 0.03 to 0.80 mg/1. The total copper, nickel,
chromium, and zinc content in suspended solids was equivalent to
as much as 2.0* mg/1, in comparison with a maximum of 1.45 mg/1
for these metals in the soluble form.
The concentration of total suspended solids in the end-of-pipe
discharge from typical chemical treatment operations ranged from
20 to 24 mg/1. Maintaining conditions so as not to exceed these
amounts requires (1) a properly designed settling and/or
clarifying facility, (2) effective use of flocculating agents,
(3) careful removal of settled solids, and (4) sufficient
retention time for settling. Of course, minimum retention time
depends on the facility size and In practice, this time ranges
from about 2 to 8 hours for plants that are able to reduce
suspended solids to about 25 mg/1. Even so, this achievement
requires very good control of feeding flocculating agents.
precipitation of Metal Sulfides
Applicability,« The sulfides of copper, nickel, and zinc are much
less soluble than their corresponding hydroxides.
Precipitation using hydrogen sulfide or soluble sulfides (Na2S)
involves toxicity problems with the excess reagent used.
However, a system has recently been developed that provides for
sulfide precipitation without the toxicity problems.(31) It
should be applicable to treatment of effluent from electroplating
operations.
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Ferrous sulfide, which has a higher solubility than the sulfides
of the metals to be precipitated is used as the precipitating
reagent. However, the solubility of ferrous sulfide is still so
small (5-10 mg/1 of sulfide ion) that the toxicity problem is
eliminated. Freshly precipitated ferrous sulfide is most
reactive and is obtained by adding an excess of a soluble sulfide
for precipitating the metals to be removed from the effluent and
then adding sufficient soluble ferrous salt to precipitate all
excess sulfide ion. The pH is normally adjusted to the range of
7 to 8, prior to precipitation, Hexavalent chromium that may be
present is reduced to Cr*3 by the ferrous iron and immediately
precipitated as the hydroxide. Therefore, no extra precipitation
steps are necessary to remove the chromium. If the extra ferrous
ions in solution are considered undesirable they may be oxidized
to Fe(IlI) which will precipitate as the hydroxide. However,
removal of iron would not be possible until after the sulfide
precipitates had been separated from the liquid. In principle,
it should be possible to precipitate metallic sulfides from metal
ion complexes that are not amenable to chemical treatment by
hydroxide precipitation, due to the lower solubilities of the
sulfides. It has been demonstrated that copper can be
effectively precipitated from the ammonia complex.
Demonstration_Status
The process described is in development stage and it is
anticipated that a demonstration plant will be built and operated
in the near future.
Combined Metal Precipitation and Cyanide Destruction
Proprietary Process E
Apgl icabi lity. This proprietary process (32) is applicable to
zinc and cadmium cyanide solutions. The metal hydroxide is
precipitated and cyanide is decomposed. Applicability depends
upon deciding whether the products of cyanide decomposition are
suitable for discharge or not. The effluent is considered
suitable for discharge to sewers in some states and may be
acceptable in certain areas for discharge to streams, h modified
process may be applicable to copper cyanide.
Pr QC es s m Pr in gig lg s^a nd_ Egui^ment
Cyanide in zinc and cadmium plating baths is destroyed by a
mixture of formalin and hydrogen peroxide according to the
formula:
CN- + HCOH + H2O2 + H2O — * CNO- + NH4 + H^C (OH) COHN2 glycolic
acid amide.
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The metal hydroxide is also precipitated. The hydrogen peroxide
is contained in the reagent (41%) which contains stabilizers and
additives to promote the reactions and help in settling the metal
hydroxide precipitate. The process may be carried out on a batch
or continuous basis, and is particularly convenient for the small
shop. Figure 6 shows the apparatus for batch treatment. To be
economical the rinse water should contain at least 55 ppm of
cyanide, and sufficient counter-flow rinses are normally
installed to assure a sufficient cyanide concentration. The
typical treated effluent contains 0.1 mg/1 of cyanide and 1 to 2
mg/1 of zinc. Table 21 shows an analysis of the products for
decomposing 19H ppm of cyanide.
Systems . This process is well established as
. -
a practical means for pollution control and is being used in
approximately 30 installations.
Water Conservation Through Control Technology
The volume of effluent is reduced if water is conserved during
rinsing operations. The solubility limit of effluent
constituents is essentially constant, so that a reduction in the
effluent volume accomplishes a reduction in the amount of
effluent constituents discharged. Water conservation can be
accomplished by in-plant process modifications requiring little
capital or new equipment, materials substitutions, and good
housekeeping practice. Further water conservation is obtained by
installing counterflow rinse tanks and ion-exchange, evaporative
recovery, or reverse osmosis systems. Other systems that may
accomplish water conservation are freezing, electrodialysis,
electrolytic stripping, carbon adsorption, and liquid- liquid
extraction.
Process Modifications
Wastes from electroplating operations can sometimes by
reduced by the following changes in electroplating processes;
(1) Elimination of copper prior to nickel and chromium
plating, especially for plating on steel
(2) Elimination of copper by increasing the thickness of
nickel
(3) Substitution of a nickel strike for a copper strike and
replacing the highrate copper cyanide solution with a copper
sulfate bath
Substitution of low- concentration electroplating
solutions for high concentration baths.
Metals remaining in solution after chemical treatment of the
effluent from a plant plating decorative copper, nickel, and
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TABLE 21- DECOMPOSITION PRODUCTS OP CYANIDE IN RINSE
WATER CD FROM A CYANIDE ZINC ELECTROPLATING
OPERATION AFTER TREATMENT WITH
PEROXYGEN COMPOUND
Products Formed Amount Formed
by Treatment Actual Cyanide Equivalent
ppnT ppro percent
Cyanate 351 265 33
Ammonia (free)
Dissolved 57 164 21
Volatilized 32 91 11
Combined Ammonia
Calc'd as NH3 95
Calc'd as glycolic 274 35
acid amide 419
794 100
^'Analysis of water before treatment:
Cyanide 794 ppm
Cyanate2 336 ppm
Ammonia2 41 ppm.
Cyanide calculated as NaCN, cyanate as NaOCN, and
ammonia as NH.
78
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4
* Jsa&a
*
FIGURE 6- BATCH TREATMENT OF CYANIDE RINSE WATERS BY
COMBINED METAL PRECIPITATION AND CYANIDE
DESTRUCTION
79
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chromium can be reduced in amount by eliminating the copper.
Some steel products can be plated directly with nickel and
chromium, especially when the quality of the steel surface is
improved. A better grade of steel or a change in mechanical
finishing methods to reduce surface roughness can sometimes
justify the elimination of copper without sacrificing high
specularity. To maintain good corrosion resistance on steel
products and eliminate copper, it may be necessary to increase
the thickness of the nickel or install duplex nickel in place of
bright nickel, which is imich better than a single layer of bright
nickel for providing maximum corrosion resistance. To maintain a
high degree of specularity in the absence of a copper plate,
leveling nickel is recommended.
The substitution of a nickel strike for a copper strike has been
adopted in several plants plating nickel and chromium on steel.
A copper sulfate solution is then utilized after nickel striking
in some cases. This change avoids copper cyanide baths and the
attendant need for oxidizing cyanide in the treatment system and
has been particularly successful for steel products.
Substitution of low-concentration electroplating solutions for
high-concentration baths has been adopted in recent years,
principally for reducing the cost of chemicals used for cyanide
destruction. The dilute solutions require less water for rinsing
when electroplated parts are transferred to rinse tanks.
Assuming a 50 percent reduction in total dissolved solids in the
plating solution and two rinse tanks in series, a 30 percent
reduction in rinse water requirements is achieved. Wastewater
constituents requiring treatment are reduced by the same amount.
Adverse effects in terms of lower efficiency and reduced
productivity per unit facility may be encountered when dilution
is adopted to conserve rinse water and reduce wastewater
constituents requiring treatment, unless other factors affecting
plating rate are modified to adjust for the effects of dilution.
Thus, dilution should not be adopted before a complete analysis
is made of all pertinent factors.
The advent of effluent limitations is expected to encourage
research and development on other processes that will eliminate
or reduce water waste. A dry process for applying chromate
coatings, which is currently being developed, may prove useful
for such a purpose. Chemical vapor deposition processes
partially developed a few years ago may be revived for plating
hard chromium.
Materials Substitutions
Noncyanide solutions, which have been developed for copper and
zinc in place of cyanide solutions, reduce the costs of treatment
by eliminating cyanide destruction, but do not eliminate
treatment to precipitate and separate the metals. The chelating
agents employed in some noncyanide baths to keep the metal in
soluble form are precipitated when rinse water waste is treated
with lime to precipitate the metals, but other agents such as
80
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e-thylene dlamine tetraacetic acid inhibit the precipitation of
zinc and contribute organic matter to the treated water waste.
Thus, the applicability of the noncyanide solutions as
replacements for cyanide baths must be considered carefully in
the light of the effluent limitation guidelines recommended in
this document.
Trivalent chromium baths have recently been introduced to the
electroplating industry. They eliminate the need for sulfur
dioxide reduction of wastewater associated with chromium plating.
The trivalent chromium baths appear to have other advantages for
decorative plating such as better throwing power, current
efficiency and plating rate. The dark color of the deposits is
cited as a disadvantage by some purchasers, however.
Nevertheless, this process modification may ultimately prove to
be significant for reducing waste treatment costs. No details
have been released on the treatment required for minimizing the
soluble chromium concentration in treated effluent.
Good Housekeeping Practices
Good housekeeping practices that reduce the waste generated in
electroplating facilities include the following;
(1) Maintain racks and rack coatings to prevent the transfer
of chemicals from one operation to another. (Loose rack
coatings are noteworthy as an example of poor practice.)
(2) Avoid overcrowding parts on a rack, which inhibits
drainage when parts are removed from a process solution.
(3) Plug all floor exits to the sewer and contain spills in
segregated curbed areas or trenches, which can be drained to
direct the spills to rinse water effluent with the same
chemicals.
(4) Wash all filters, pumps and other auxiliary equipmentin
curbed areas or trenches, which can be drained to direct the
wash water to a compatible holding tank or rinse water
stream,
(5) Install anti-syphon devices on all inlet water lines to
process tanks.
(6) Inspect and maintain heating and cooling coils to avoid
leaks.
<7) Inspect and maintain all piping installed for wastewater
flow, including piping from fume scrubbers,
Water Conservation by Reducing Dragout
81
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Dragout is defined as solution on the workpiece carried
beyond the edge of the plating tank. The dragout of concentrated
solution from the plating tank can vary over a wide range
depending on the shape factor of the part. A value of 16.3
liters/1000 sq m (0.4 gal/1000 sq ft) (33) is considered a minimum
for vertical parts that are well drained. The practical range
for parts of various shapes that are well drained is about 40 to
400 liters/sq m (1 to 10 gal/1000 sq ft).
Dragout_::ileduction. Water used for rinsing can be conserved by
(1) improving the racking procedure to improve drainage from
surfaces over the process tank, prior to transfer to the
subsequent rinse tank, (2) increasing the drainage time over the
process tank, (3) reducing the viscosity of the process solution
by diluting it or increasing its temperature, (4) adding a
wetting agent to the process solution to reduce surface tension,
(5) installing fog nozzles above the process tank to return a
part of the solution remaining on work surfaces to the process
solution, and (6) installing a drip-save (reclaim) tank between
the process and rinse stations to collect dragout that is pumped
back to the process solution. A mixture of air and water is
utilized in one version of a fog nozzle claimed to be especially
effective for removing most of the solution from surfaces lifted
above process tanks. With the above techniques, the water needed
for rinsing can be reduced as much as 50 to 60 percent. Detailed
comments on these dragout reduction techniques appear in
Reference 34.
Reduction of dragout with the above methods is not without
problems. By returning chemicals to the plating tank, impurities
tend to build up in the plating solution. Therefore,
purification systems, such as ion exchange, batch-chemical
treatments, and/or electrolytic purification are required to
control impurities. The purification systems create some
effluents which must be treated prior to end-of-pipe discharge.
Water Conservation During Rinsing
when effective chemical treatment exists, reduction in
pollutional load can be accomplished by reducing the water use in
the facility. The principal water use is for rinsing. Use of
only that water needed for effective rinsing based on dissolved
solids would represent good practice.
Water conservation procedures that are used after processed work
is transferred to a rinse tank include (1) adding a wetting agent
to the rinse water, (2) installing air or ultrasonic agitation
and (3) installing counterflow rinses whereby water exiting the
last tank in the rinsing operation becomes feed water for the
preceding rinse. With two counterflow rinses, water consumption
is reduced 96 percent in comparison with a single rinse, with
equivalent rinsing effectiveness. Use of conductivity meters in
the final rinse provides automatic control of water use according
-------
to need. Rinse water flow is shut off automatically when no work
is being processed. Excessive use of water can also be avoided
by use of flow restrictors in the water feed lines.
Although multitank, counterflow rinsing imposes capital
investment costs for tanks, pumps, and floor space, these costs
are compensated by a savings in water (and sewer) charges.
Further incentive is provided when regulatory agencies require
pollutional control. When end-of-process chemical treatment is
used, design of wastetreatment facilities usually indicates the
economic advantage of reducing rinse-water flow by installing two
or more counterflow rinses.
Because waste-treatment facilities are usually over- designed to
handle future expansion in production, there is a tendency to use
the water flow capacity of the treatment facility whether or not
it is needed for effective rinsing. Furthermore, rinse water
flows set by an orifice are not always turned off when plating
production is shut down. In the case of an overdesigned
installation, it is probably more economical to reduce rinse
water usage by use of good rinsing practice than to increase
water-treatment facilities in the event of an increase in
production.
Rinsing can be carried out beyond the point consistent with good
practice, even though there is an economic incentive to save
water. The result is unnecessary pollution. Typical
concentration levels permitted in the rinses following various
process tanks, should not be decreased unless definite quality
problems can be associated with the dissolved solids
concentrations listed below for representative rinsing
systems: (35)
Max Dissolved Solids
j_^_ in_Final__.Rinse * fflg/1
Alkaline cleaners 750
Acid cleaners, dips 750
Cyanide plating 37
Copper plating 37
Chromium plating 15
Nickel plating 37
Chromium bright dip 15
Chromate passivating 350-750
A Watts-type plating bath typically contains 270,000 mg/1 of
total dissolved solids. Obtaining 37 mg/1 in the final rinse
requires 27,600 liters (7300 gallons) of rinse water if a single
rinse tank is used, in order to dilute 3.78 liters (1 gallon) of
a Watts-type plating solution containing 270 g/1 of dissolved
solids. The same degree of dilution in a final rinse tank may be
obtained with less water by use of series and counterflow
arrangement of two or more rinse tanks. If the tanks are
83
-------
arranged in series and fresh water is fed in parallel to each
tank in equal volume, the ratio, r of rinse water to dragout is;
r = (CQ/CF) */w.
where Co = concentration in the process solution CP =
concentration in last rinse tank and n = number of rinse tanks.
If the tanks are arranged in the same way but flow proceeds from
the last rinse tank to the first rinse tank (counterflow),
,
r = (CO/CF)
By feeding water to counterflow tanks instead of in series, the
reduction in water varies n-fold. Values of n calculated for
several rinsing combinations, using the Co and CF values given
above for a nickel bath are as follows:
Rinse_Combinatipn Riase. Ratiox r_
Single rinse 7300
Two rinses, parallel feed 171
Three rinses, parallel feed 58.3
Two rinses, counterflow feed 85.5
Three rinses, counterflow feed 19.5
There is a significant reduction in water use by addition of a
second rinse tank, and at least two rinse tanks can be considered
normal practice. These should best be fed in counterflow.
Counterflow rinse tanks increase the concentration of a metal or
another constituent in the first rinse tank following the plating
or process bath. The water in the first rinse tank can be used
to supply make-up water for the plating bath. As the
concentration in the first rinse tank increases, more of the
drag-out from the plating bath can be returned to the bath in the
make-up water, and less will require treatment and/or disposal.
Therefore, the addition of countercurrent rinse tanks can
decrease both the volume of water to be treated and the amount of
dissolved metal that must be removed, at least in some cases.
The rate of evaporation from the plating bath is a factor in
determining how much make-up water must be added. Operating a
bath at a higher temperature will allow more of the drag-out to
be returned to the bath because of the higher rate of
evaporation. However, the temperature at which a bath may be
operated is sometimes limited because of the decomposition of
bath components. Progress has been made in developing bath
components that allow higher bath temperatures to be used. For
example, brighteners for zinc cyanide baths have been
84
-------
developed(36) which allow bath operation at 50°C (120*F) as
compared to 32°C (90 ° F) for baths using older aldehyde-type
brighteners. Thus, the new brighteners permit the return of more
of the dragout to the plating bath and a lessened load on the
waste treatment system, in addition to what other processing
advantages they may offer.
Water Conservation by Ion Exchange
&BB! icabil ity Ion exchange is currently a practical com-
mercially accepted method for the in-process treatment of (1) raw
water, (2) plating baths, and (3) rinse waters. Raw water is
treated to provide de-ionized water for both makeup and critical
final rinsing operations. Plating baths are treated to remove
impurities, i.e., removal of nickel ions from a chromic acid bath
with a cation exchange resin. Rinse waters are treated to
provide water that can be returned to the process solution. The
concentrated regenerant can be chemically treated more easily
than the original volume of rinse water and in some cases the
chemicals can be recovered and returned to the bath. The in-
process treatment of chromium and nickel plating effluents by
ion-exchange techniques are the more economically attractive
treatment operations currently being carried out. Ion exchange
also is beginning to find increased use in combination with
evaporative and reverse-osmosis systems for the processing of
electroplating rinse waters.
AdvantagesandLimitations. Some advantages of ion exchange for
"treatment~~of~"plating effluents are as follows:
(1) Ion exchange is an economically attractive method for
the removal of small amcunts of metallic impurities from
rinse waters and/or the concentration for recovery of
expensive plating chemicals,
(2) Ion exchange permits the recirculation of a high-quality
water for reuse in the rinsing operations, thus saving
on water consumption.
(3) Ion exchange concentrates plating bath chemicals for
easier handling or treatment or subsequent recovery or
disposal operations.
Some limitations or disadvantages of ion exchange for treatment
of plating effluents follow:
(1) The limited capacity of ion-exchange systems means that
relatively large installations are necessary to provide
the exchange capability needed between regeneration
cycles.
85
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(2) Ion-exchange systems require periodic regeneration with
expenditures for regenerant chemicals. Unless
regeneration is carried out systematically, leakage of
undesirable components through the resin bed may occur.
In addition, the usual treatment methods must be
employed to dispose of the regenerated materials,
(3) Cyanide generally tends to deteriorate the resins, so
that processing of cyanide effluents (except, for very
dilute solutions) does not appear practical at the
present time.
(^) Resins slowly deteriorate with use and the products of
deterioration can contaminate the water.
PrQcess_mijPrincijples... and Eguiement. Ion exchange involves a
reversible interchange of ions between a solid phase and a liquid
phase. There is no permanent or substantial change in the
structure of the solid resin particles. The capacity of an ion-
exchange material is equal to the number of fixed ionic sites
that can enter into an ion-exchange reaction, and is usually
expressed as milliequivalents per gram of substance. lon-
exchange resins can perform several different operations in the
processing of wastewater, including:
(1) Transformation 'of ionic species
(2) Removal of ions
(3) Concentration of ions.
The performance of some of these functions is illustrated in
Figure 7, which is a generalized schematic presentation of the
application of ion exchange to treatment of electroplating
effluents.(37,38) In practice, the solutions to be treated by
ion exchange are generally filtered to remove solids such as
precipitated metals, soaps, etc., which could mechanically clog
the resin bed. Oils, organic wetting agents, brighteners, etc.,
which might foul the resins, are removed by passage through
carbon filters.
During processing, the granular ion-exchange resin in the column
exchanges one of its ions for one of those in the rinse water or
other solution being treated. This process continues until the
solution being treated exhausts the resin. When this happens,
solution flow is transferred to another column with fresh resin.
Meanwhile, the exhausted resin is regenerated by another chemical
which replaces the ions given up in the ion-exchange operation,
thus converting the resin back to its original composition. With
a four-column installation consisting of two parallel dual-bed
units, as shown in Figure 7, the ion-exchange process can be
applied continuously by utilizing the regenerated units while the
exhausted units are being regenerated.
86
-------
Waste from
cor laminated
rinse overflow
Waste-water
reservoir
Filter
/-K
Filter
To clean-water
reservoir and
process rinse tanks
Cation
Anion
V V
Cation
Anion
FIGURE 7. SCHEMATIC PRESENTATION OF ION-EXCHANGE APPLICATION FOR
PLATING-EFFLUENT TREATMENT (7,25)
-------
Practical_Ogerating-_S^st.em3. Figure 8 shows a schematic drawing
of the ion-exchange system used in Plant 11-7 to handle a flow
ranging from 2,100 to 4,000 gph of chromium rinse water
containing 30 to 250 ppm of hexavalent chromium. The unit saves
at least 150rOOO liters/d (40,000 gpd) and provides a source of
deionized water throughout the plant for preparing plating
solutions where good quality water is required. The pure water
recycled to the chromium rinse tanks is useful for avoiding
spotting of chromium-plated parts. Regenerated solution from the
anion-exchange unit is treated by reducing the chromium to Cr*3
and precipitating it. Regenerated solution from the cation-
exchange unit is combined with the acid-alkali stream for
treatment.
Cation-exchange resins are used widely throughout the industry
for removing nickel, trivalent chromium, and other impurities
from chromium plating baths. Cyanide may be absorbed on ion-
exchange resins, but there is danger of leakage of cyanide
through the system. An improved three bed system consists of
strongly acidic, weakly basic, and strongly basic layers (39) .
In this system the weak base resin provides a high capacity for
cyanide adsorption and the strong base resin provides a back up
to take care of cyanide leakage.
Demonstration __ Status « An ion-exchange system utilizing a short
30 minute cycle, "including a 3 to 4 minute back wash, to recover
chromic from rinse water has been in operation over a year^ (40) .
The resin undergoes very little deterioration since the chromic
acid is not deeply absorbed into the resin during such a short
cycle.
I gnLrlxchange^fprTM.ixediigf fluent. An installation for handling
6,300 gph of wastewater containing nickel, chromates, chlorides
and sulfates was installed for recovering 96 percent of the water
(32) . The cost saving in water was more than three times the
cost of operation.
Water Conservation by Evaporative Recovery
When rinse water from one type of bath is
distilled in an evaporative unit, the concentrate may be returned
to the plating bath and the distillate to the corresponding rinse
tank, which is useful for closing the loop on a single plating
operation. The economics of distillation, from the standpoint of
either investment or operating costs imposes a constraint on the
size range of distillation equipment, Units with a capacity of
the order of 300 gph are used in practice. Such a low rate of
flow of rinse water is achieved in many plating operations only
by the use of at least three countercurrent rinses, which by
itself reduces the wastewater. Evaporative recovery units for
all of the rinse cycles would reduce the effluent to zero. So
far, recovery units have been installed on rinse tanks following
88
-------
Cu-Ni-Cr
manual hoist
line
Counter-
flow
rinses
Well
water
as needed
15 gpm
Cation
resin
Stevens
Ni-Cr
automatic
line
Hard-
chromium
plating
Counter-
flow
rinses
10 gpm
Counter-
flow
rinses
9 gpm
Anion
resin
Cation
resin
Anion
resin
Deionized water
FIGURE 8 . SCHEMATIC PRESENTATION OF ION-EXCHANGE OPERATION
AT PLANT 11-8
89
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plating baths in order to recover plating chemicals and return
them to the bath and thereby reduce plating costs. The units
have not been installed on cleaner or acid dip lines because the
cost of chemicals is not sufficient to make recovery worthwhile.
Evaporation is a firmly established industrial procedure for
recovering plating chemicals and water from plating waste
effluents, commercial units for handling zinc, copper, nickel,
chromium, and other metal plating baths have been operating
successfully and economically for periods of one to 10 years or
longer. Packaged units for in-plant treatment of plating wastes
are available from many manufacturers.
Advantages and Limitat ions. The following are some of the
advantages of using evaporation for handling of plating waste
effluents:
(1) Recovers expensive plating chemicals, which were either
lost by discharge to a sewer or stream or which had to be
treated or destroyed prior to disposal; chemicals
concentrated to plating strength can be returned to the
plating tank.
(2) Recovers distilled water for reuse in the rinse
operations, thus lowering water and sewage costs.
(3) Eliminates or greatly minimizes the amount of sludge
formed during chemical treatment and eliminates or reduces
the amount requiring disposal by hauling or lagooning,
(4) The use of vacuum allows evaporation to occur at
relatively low temperatures (e.g., 110*F) so that destruction
of cyanides or other heatsensitive materials is lessened.
(5) The technology of evaporators (conventional and vapor
recompression units) is firmly established, so their
capabilities are well known and their performances should be
readily predictable and adaptable to plating effluent
handling.
some of the limitations or disadvantages of evaporative recovery
systems are given below:
(1) The rinse water saving [e.g., 1100 1/hr (300 gph) ] is
rather small, and by itself does not significantly reduce the
rinse water load on the chemical treatment plant.
(2) Evaporative units have relatively high capital and
operating costs, especially for the vacuum units. Steam and
coolant water are required.
(3) The evaporative units are fairly complex and require
highly trained personnel to operate and maintain them.
90
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(H) Separate units are required for handling the waste
effluent from each line, as various solutions, such as zinc,
nickel, copper, chromium, cannot be mixed for chemical
recovery.
The advantages offered by evaporative recovery outweigh the
disadvantages when existing chemical treatment facilities are not
available. Evaporative recovery is a promising and economical
method currently available for handling plating waste effluents
and limiting treatment plant size. Where existing chemical
treatment (cyanide destruction, chromate reduction, and chemical
precipitation) facilities are operating at less than capacity,
the economics and practicality of installing new evaporative
equipment must be closely evaluated. The small decrease in the
rinse water effluent e.g., 1100 1/hr (300 gph) by itself does not
warrant the installation of an evaporative system. The savings
produced by the recovery of plating chemicals plays the
significant role in judging the overall merits of the evaporative
system for a specific operation.
Process , ......... PringiBles^ ........ _ ..... afld_E(|^Lj.S.B1SBfe* ^ representative closed loop
"system for recovery of chemicals and water from a plating line
with a single-effect evaporator is shown in Figure 9. A single-
effect evaporator concentrates flow from the rinse water holding
tank. The concentrated rinse solution is returned to the plating
bath, and distilled water is returned to the final rinse tank.
With the closedloop system, no external rinse water is added
except for make-up of atmospheric evaporation losses. The system
is designed for recovering 100 percent of the chemicals, normally
lost in dragout, for reuse in the plating process,
Single-, double-, and multiple-effect evaporators, and vapor -
recompression evaporator units are used for handling plating
effluent. Open-loop and combined evaporation (i.e., evaporation
combined with ion- exchange, reverse-osmosis, or other systems)
are also employed for handling plating effluent.
A single-effect evaporator is preferred, if relatively
unsophisticated operating personnel are involved, or low initial
capital outlay is desired. It's the simplest in design and
therefore the easiest to operate. However, it is less economical
than a double effect or vapor-recompression unit with regard to
utility costs (^1). A double-effect evaporator should be
considered when lower operating cost is desired with a modest
increase in capital investment.
A vapor-recompression evaporator should be considered if no steam
or cooling water is available. Where utilities for a
conventional steam evaporator are available, the high initial
cost of the vapor recompiression unit is not economically
justified. Its operating cost is the lowest of the three
systems. Its dependence on an expensive and complex mechanical
compressor is the main disadvantage.
91
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© KEClKCUUmOH.COHCLHTRATC
OI$TILl*IF
0
FIGURE 9 . REPRESENTATIVE CLOSED-LOOP SYSTEM FOR RECOVERY
OF CHEMICALS AND WATER WITH A SINGLE-EFFECT
EVAPORATOR
92
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Some sources report considerable maintenance and down time and
have dispensed with use of evaporator units. Other sources
report little or no trouble and are very satisfied with the
operation. It appears that the units can perform very
satisfactorily if the installation is properly engineered, and if
preventive maintenance and trouble-shooting are carried out by
knowledgable personnel,
In some instances, evaporation procedures must be used in
combination with chemical or other methods in order to handle
small amounts of impurity build-up (e.g., brighteners,
carbonates, extraneous metal ions, etc,, in closed-loop
operation) or for treatment of minor bleed-off streams (open-
loop) ,
Atmospheric evaporation, which uses air flow through packing
media in an evaporator, can concentrate plating solution such as
chromic acid up to 480 g/1 (4 Ib/gal) (42) . One manufacturer (43)
has introduced a new concept for evaporative recovery. A glass
shell and tube heat exchanger is mounted vertically and the
solution is fed through the bottom. The boiling causes liquid
surges that produce a "rising film" effect and an improvement in
heat transfer. Vapor and liquid overflow the top of the tubes
and are separated in a cyclone. Water with less than 0.05 ppm of
chromic acid has been produced from chromium plating rinse water,
Pr act i cal._ _0per at ing ,_^S^ stems. Extensive use is made of
evaporators in Plant 20-14, where three units with capacities of
380, 380, and 190 1/hr (100, 100, and 50 gph) are used to
completely close the copper cyanide, nickel, and chromium rinse
lines respectively. Only the cleaning and acid pickling lines
are open and it is roughly estimated that the combined effluent
volume from them may be of the order of 11,300 1/hr (3000 gph).
The alkali rinse is run directly to the sewer and the acid line
is neutralized and run to the sewer without clarification. Small
spills and washes are treated chemically. Rearrangement of
cleaner and acid dip rinse tanks to counterflow operation could
reduce the volume of effluent to a very low level and
installation of an evaporator would reduce it further. In
contrast to the plating tanks, the cleaners and acids must be
discarded periodically so that a completely closed loop on these
lines does not seem possible. However, there is no economic
incentive to change the present arrangement in this plant to
reduce the present effluent volume. One manufacturer has
installed over 100 evaporative recovery systems in metal
finishing shops,
Figure 10 illustrates an open-loop, partial recovery evaporation
system, which is suitable for plating installations where there
is an insufficient number (i.e., less than three) rinses. The
data shown in Figure 11 are for a cyanide plating line. A small
portion of the cyanide dragout that accumulates in the final
rinse is not recirculated to the evaporator for concentration.
The circulation loop through the evaporator is opened by creating
93
-------
EOO .".PH MAKC UP WATER
tOSPH
JAZ OX/CM..
20GPH
IJK., •'r.^-C.
f 0720VCAL.
1ST R1N-3E
TA.MK
W* OI CfcU
uoo */WK,
Qfc**
RECOVEfW
2NOHINSE
TANK
*A OlAr. (K
' i^o'Js
TO OESTRUSt
OH66WKR
! „
¥
"|... -• •y.wj^f' cot
iitettiwNtr^i-CvEL (
TkNK CONTRCH,
.NOCMSCH . I—
==|5
20CPH
^ y
tj—cW
!N
aEPWWTOR
2OOCPH
CONCSMTRAte l/"^?
diitJt-ATio.-i v3 j
PUMP \=-<
CT^j
Tit
STEAM
HIGf M
CONBEKSME
FIGURE 10. REPRESENTATIVE OPEN-LOOP EVAPORATIVE RECOVERY
SYSTEM(34)
94
-------
FIGURE U.
CLOSED LOOP SYSTEM FOR METAL FINISHING. PROCESS WATER
AT ROCK ISLAND ARSENAL
-------
another flow path for the cyanide. With only two rinse tanks,
the open-loop system can be operated economically, because only
about H percent of the dragout is lost; this dragout must be
treated by some appropriate chemical method before disposal.
Demonstration Status
Atmospheric evaporators have been shown to be practical for
recovering chromic acid from spray mists collected in chromium
plating venting and scrubbing units. A cation exchanger is used
to purify concentrated chromic acid before it is recycled to the
plating bath. Several units of the glass "rising film"
evaporator are being field tested in applications involving
chromic acid solutions.
water conservation by Reverse osmosis
Applicability. Reverse osmosis uses a pressure differential
across a membrane to separate a solution into a concentrate and a
more dilute solution that may approach the purity of the solvent.
It therefore accomplishes the same type of separation as
distillation and has been applied in plating installations in the
same manner. Small units under 300 gph have been installed to
recover plating bath chemicals and make closed-loop operation of
a line possible. There are limitations on the acidity and
alkalinity of solutions suitable for treatment by reverse osmosis
that eliminate some alkaline baths and chromic acid baths from
consideration unless modifications are made to the solutions
prior to treatment. A recently designed system for Plant 11-22
offers promise that large capacity reverse osmosis systems are
possible and therefore not subject to the size constraints of
evaporative systems. If so, they should play a key role in the
design of plants that will have no liquid effluent.
Most of the development work and commercial utilization of the
reverse osmosis process especially for desalination and water
treatment and recovery has occurred during the past 10 years.
There is a steadily growing number of commercial installations in
plants for concentration and recovery of plating chemicals along
with recovery of water under essentially closed-loop conditions.
Most of the existing commercial installations are for treatment
of nickel plating solutions, since reverse osmosis is especially
suited for handling nickel solutions and also because of the
favorable economics associated with recovery and reuse of
expensive nickel chemicals. Commercial reverse osmosis units for
handling acid zinc and acid copper processes also have been
installed, however. Laboratory and pilot-plant studies directed
at handling cyanide and chromium-type effluents are under way.
Reverse osmosis is especially useful for treating rinse water
containing costly metals and other plating salts or materials.
Generally, the purified water is recycled to the rinse, and the
96
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Plating
tank
Parts
Rinse
1
High-
pressure
pump
Filter
Parts
Rinse
2
Low-pressure
pump
Concentrate
Reverse-osmosis
unit
Permeate
Parts
Makeup
water
FIGURE 12 ,
SCHEMATIC' DIAGRAM OF THE REVERSE-OSMOSIS PROCESS
FOR TREATING PLATING EFFLUENTS
-------
concentrated salts to the plating bath. In instances where the
concentrated salts cannot be recycled to the plating tank,
considerable savings will be achieved because of the reduced
amount of waste-containing water to be treated.
Advantages ,and__LimJ.tationg« Some advantages of reverse osmosis
for handling plating effluents are as follows:
(1) Ability to concentrate dilute solutions for recovery of
plating salts and chemicals
(2) Ability to recover purified water for reuse
(3) Ability to operate under low power requirements (no
latent heat of vaporization or fusion is required for effecting
separations; the main energy requirement is for a high-pressure
pump) .
(H) operation at ambient temperatures 60 to 90° F)
(5) Relative small floor space requirement for compact high-
capacity units.
Some limitations or disadvantages of the reversed osmosis
process for treatment of plating effluents are listed below:
(1) Limited temperature range for satisfactory operation.
(For cellulose acetate systems the preferred limits are 65 to 85*
Fj higher temperatures will increase the rate of membrane
hydrolysis, while lower temperature will result in decreased
fluxes but not damage the membrane) .
(2) Inability to handle certain solutions (strong oxidizing
agents, solvents and other organic compounds can cause dissolu-
tion of the membrane).
(3) Poor rejection of some compounds (some compounds such as
borates and organics of low molecular weight exhibit poor
rejection).
(4) Fouling of membranes by slightly soluble components in
solution,
(5) Fouling of membranes by feeds high in suspended solids
(such feeds • must be amenable to solids separation before
treatment by reverse osmosis).
(6) Inability to treat highly concentrated solutions (some
concentrated solutions may have initial osmotic pressures which
are so high that they either exceed available operating pressures
or are uneconomical to treat).
98
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Process Principles, and Eguipment. Water transport in reverse
osmosis (RO) is opposite to the water transport that occurs in
normal osmosis, where water flows from a less concentrated
solution to a more concentrated solution. In reverse osmosis,
the more concentrated solution is put under pressure considerably
greater than the osmotic pressure to drive water across the
membrane to the dilute stream while leaving behind most of the
dissolved salts. Salts in plating baths such as nickel sulfate
or copper sulfate can be concentrated to solutions containing up
to 15 percent of the salt, by weight (4*1,45) .
Membrane materials for reverse osmosis are fairly limited and the
bulk of the development work has been done with specially
prepared cellulose acetate membranes, which can operate in a pH
range of 3 to 8 and are therefore useful for solutions that are
not strongly acid or alkaline, i.e., rinses from Watts nickel
baths. More recently, polyamide membranes have been developed
that will operate up to a pH of 12, and several of these units
are operating in plants for the treatment of cyanide rinse
waters.
Figure 11 is a schematic presentation of the reverse osmosis
process for treating plating-line effluent. The rinse solution
from a countercurrent rinse line is pumped through a filter,
where any suspended solids that could damage or foul the membrane
are removed. The rinse solution is then raised to the operating
pressure by a high pressure pump and introduced into the reverse
osmosis unit. The concentrated salt stream is returned to the
plating tank, while the dilute permeate stream is returned to the
second rinse tank. Currently, several different configurations
of membrane support systems are in use in commercial reverse
osmosis units. These include plate and frame, tubular, spiral
wound, and hollow fine fiber designs,
Practical Operating: Systems. Plant 13-2 has installed a reverse
osmosis unit on the rinse line of a 6800 liter (1800 gal) bright
nickel solution. Solution from a dragout tank immediately
following the plating bath is returned directly to the plating
bath. Water in the succeeding rinse tanks,containing
approximately 25 ppm of nickel, is pumped through a 50-micron
prefilter and six reverse osmosis modules at the rate of 450 1/hr
(120 gph). Concentrate, at the rate of 23 1/hr (6 gph), is
returned to the plating tank and 445 1/hr (118 gph) of water are
returned to rinse tanks. The unit is reverse flushed once every
two weeks, which produces 23 liters (6 gallons) of waste that is
sent to a sludge holding tank. Otherwise the system operates as
a closed loop. Life of the modules is estimated to be 2-1/2
years. This system is typical of the systems that have been
installed until recently.
A waste-treatment plant designed to produce no liquid effluent
has been recently installed at the Rock Island Arsenal (Plant 11-
22). Key components in the process are two reverse osmosis units
operating in parallel and capable of handling 26,000 1/hr (6800
-------
gph) of effluent. This flow rate is typical for a medium-large
plating installation, so that reverse osmosis should be capable
of treating total wastewater rather than being used for chemical
recovery on individual lines where water volume is much lower.
Plant 11-22 had no treatment facilities prior to installation of
the new unit. Dilution of plating plant effluent by other
effluents at the Arsenal reduced concentrations of pollutants to
very low levels. The waste-treatment system could therefore be
designed from scratch rather than as an add-on to an existing
system. The system that was chosen uses chemical treatment
followed by reverse osmosis. The flow diagram in Figure 12
describes Plant 11-22*s zero effluent system. The small amount
of cyanide is pretreated before being combined with streams from
the chromium, acid, alkali, acid copper and nickel baths.
Hexavalent chromium is reduced in the neutralizer tank at pH 8.5.
Metal oxides are precipitated at the same time. Effluent from
the clarifier goes through a reverse osmosis system. Each of the
parallel assemblies contain 26 units that are operated so that 18
units operate in parallel, followed by 6 units in parallel,
followed by 2 units in parallel. Thus, these three parallel
systems operate in series with each other.
A smaller reverse osmosis unit is used in the plating plant to
recover chromium dragout. The acidity of the rinse water is
reduced somewhat to prevent deterioration of the reverse osmosis
membrane. A deionizer is then used to remove salts formed by the
partial neutralization, after which the chromium concentrate can
be returned to the plating tank.
Water Conservation by Freezing
Applicability. The freezing process would be capable of
recovering metal and water values from plating rinse water to
permit essentially closed-loop-type operation if fully developed.
The feasibility of using freezing for treatment of plating rinse
waters was demonstrated on a laboratory scale using a mixed
synthetic solution containing about 100 mg/1 each of nickel,
cadmium, chromium, and zinc, along with 30,000 mg/1 of sodium
chloride. Greater than 99,5 percent removal of the metallic ions
was achieved in the experiments, with the purified water product
containing less than 0.5 mg/1 each of the individual plating
metals. The separation tests were carried out using the 9500
1/hr (2500-gpd) at a pilot-plant unit.
Process Principles and Equipment. The basic freezing process for
concentration and recovery of water from plating effluents is
similar to that used for recovery of fresh water from the sea. A
schematic diagram of the treatment of plating rinses by the
freezing process is shown in Figure 13 (46,47). The contaminated
reuse water is pumped through a heat exchanger (where it is
100
-------
O
Purified
water
To rinse
tank
Pump
Cooling
water
Heat exchanger
Melter/
condenser
Refrigerant
Concentrate
-------
cooled by melted product water) and into a freezer. An
immiscible refrigerant {e.g., Freon) is mixed with the reuse
water. As the refrigerant evaporates, a slurry of ice and
concentrated solution is formed. The refrigerant vapor is pumped
out of the freezer with a compressor. The slurry is pumped from
the freezer to a counterwasher, where the concentrated solution
adhering to the ice crystals is washed off. The counterwasher is
a vertical vessel with a screened outlet located midway between
top and bottom. Upon entering the bottom, the slurry forms a
porous plug. The solution flows upward through the plug and
leaves the counterwasher through the screen. A small fraction of
the purified product water (less than 5 percent) flows
countercurrently to the ice plug to wash off concentrated
solution adhering to the ice. The ice is pumped to a condenser
and melted by the release of heat from the refrigerant vapor
which had been originally evaporated to produce the ice, and
which had been heated by compression to a saturation temperature
higher than the melting point of the ice,
Because of the pump work, compressor work, and incomplete heat
exchange, a greater amount of refrigerant is vaporized than can
be condensed by the melting ice. Consequently, a heat-removal
system is needed to maintain thermal equilibrium. This system
consists of a compressor which raises the temperature and
pressure of the excess vapor to a point where it will condense on
contact with ambient cooling water.
The freezing process offers several advantages over some other
techniques. Because concentration takes place by freezing of the
water in direct contact with the refrigerant, there is no heat-
transfer surface (as in evaporation) or membrane (as in reverse
osmosis) to be fouled by the concentrate or other contaminants.
Suspended solids dc not affect the freezing process and are
removed only as required by the end use to be made of the
recovered products.
The heat of crystallization is about 1/7 the heat of
vaporization, so that considerably less energy is transferred for
freezing than for a comparable evaporation operation. Because
freezing is a low-temperature process, there will be less of a
corrosion problem than with evaporation, and less expensive
materials of construction can be employed. The freezing process
requires only electrical power, as opposed to the evaporation
process which also requires steam generating equipment. The cost
of the freezing method may be only 1/3 that for evaporative
recovery.
_Practical__ Operating Sy stems. No commercial utilization of
freezing for treatment of waste water from metal finishing is
known in the United States. It is understood that practical
systems exist in Japan, however.
102
-------
______ __ ______ No demonstrations are in progress in metal
finishing plants. However, a 9500 liters/day (2500 gpd) unit is
in operation to demonstrate desalination of water.
Hater^Conseryatioji ........ bv_Electrodialvsis
fef • Electrodialysis removes both cations and anions
from solution and is most effective with multi-valent ions (48) .
Therefore, it is capable of reducing the concentration of copper,
chromium, nickel, and zinc ions from solution whether these
metallic ions are complexed or not. chrpmate and cyanide ions
may also be removed.
Process __ Principles and Equipment, The simplest electrodialysis
system consists of an insoluble anode and an insoluble cathode
separated by an anion permeable membrane near the anode and a
cation permeable membrane near the cathode. An anode chamber,
cathode chamber, and middle chamber are thereby formed. Upon
electrolysis anions pass from the middle chamber tq the anode
compartment and cations pass from the middle chamber to the
cathode compartment. The concentration of salt in the central
compartment is thereby decreased. By employing several anion and
cation permeable membranes between the electrodes several
chambers are created, h stream may then be run through several
of these chambers in such a pattern that the concentration is
reduced in each successive chamber. Another stream is run
through chambers in which the concentration is successively
increased. The net effect is similar to that of a continuous
moving bed ion-exchange column with electrical energy used for
regeneration rather than chemicals.
Pr act ica 1 ...... Oper at ing,,... Systems . No practical operating systems have
been reported. However, development has resulted in several
demonstrations, discussed below.
fiS£}°IlS£E^ti2S _ Status, Several demonstrations have shown that
electrodialysis is a promising method. Further development and
use of the method may be expected. Copper cyanide rinse water
may be concentrated sufficiently to be returned to the bath by
using two units on a double counterflow rinse system, i.e.,
between the first and second rinse tank and between the bath and
first rinse tank.
Water_ Congeryation by.Ion-Flotation Techniques.
Applicability. Ion-flotation techniques have not been developed
for application to plating rinse water effluents. If
103
-------
successfully developed into a practical method for plating
effluent treatment, ion flotation offers possibilities of
reducing the amount of water discharged by 60 to 90 percent for
some plating operations. These savings are based on results of
small-scale laboratory studies on solutions containing cyanides
or hexavalent chroirium.
Process^^Principj.es [:| and ^Eguipment. Separation of ions from
aqueous solutions by a flotation principle is a relatively new
concept, first recognized about 25 to 30 years ago. In the ion-
flotation operation a surface active ion with charge opposite to
that of the ion to be concentrated is added to the solution and
bubbles of air or other gas are introduced into the solution to
form a froth of the surface-active material. The foam is
separated and collapses to form a scum containing an ion-
concentrate. Ion flotation combines the technologies of mineral
flotation and ion-exchange. A schematic diagram of an ion-
flotation cell is shown in Figure 14.
Experimental results indicate that 90 percent of the hexavalent
chromium in a 10 to 100 mg/1 solution can be removed with primary
amine surface active agents (49). However, the amine suffered
deterioration when regenerated for re-use, since the removal
efficiency dropped to 60 percent after two regenerations of the
amine.
Grieves, et al.,(50) have demonstrated the feasibility of using
ion flotation on dichromate solutions with a cationic surfactant
(ethylhexadecyldimethylammonium bromide). A continuous operation
with a retention time of 150 minutes was devised. The feed
stream contained 50 mg/1 of dichromate. Approximately 10 percent
of the feed stream was foamed off to produce a solution
containing 450 mg/1 of dichromate, while the stripped solution
contained 15 mg/1.
Cyanides have been removed from dilute solutions with mixed
results. The extraction efficiency from a cadmium cyanide
solution containing 10 ppm of cyanide was 57 percent, using
primary, tertiary, and quaternary ammonium compounds as
collectors. Extraction efficiencies for nickel and iron cyanide
solutions were approximately 90 percent.
PracticajL _Qp§rating_Systems. There are no practical operating
systems.
Demonstration Status. The process has not been demonstrated in
an operating plant,
Water Conservation byElectrolyticStripping
104
-------
Air in
-* —
Foam concentrate
take-off
Purified
solution -*
removal
Injection port
for collector »~
agent
I
6'oS
»«/
8 t
*1
D»'
>.:
» *•
'.<' r
0,^
tlfto1*
~N
1
»
^u»*w~J^~*-w™
f-
\
f*f~
f^***t*^s*r*?*f
**^*jr*^f~*****^*f*f
in
!•';
!'!•
$
.'0
•V
o »
Air out
'»«'••
rs^rit
•**•-.
— Foam level
— Solution level
X' • • Solution scimplincj
nnr4
pori
FIGURE 14.
SCHEMATIC DIAGRAM OF ION-FLOTATION CELL FOR
TREATMENT OF PLATING EFFLUENT
105
-------
a,pplicability. Electrolytic stripping is not in general use for
copper, nickel, chromium or zinc, although some procedures have
been employed for recovering precious metals. Recent technical
developments suggest that they can be used to reduce heavy metal
concentrations in the effluent to very low values as well as
provide for recovery of the metals,
Process ± Principles and Equipment. In order to strip a solution
by electrodeposition it is necessary that the metallic ions in a
dilute solution reach the cathode surface at a sufficient rate so
that essentially all of the ions can be deposited in a reasonable
time, Surfleet and Crowle(51) have discussed several methods of
accomplishing this. One method called the "integrated11 system
uses baffles in a tank to create a very long path through which
the water may be recirculated at a high velocity. The method is
suitable only for metals having a relatively high limiting
current density for dilute solutions, such as gold, silver, tin.
The fluidized bed electrode is a bed of metal spheres or metal-
coated glass spheres that is fluidized by pumping the dilute
solution through it and causing an expansion of 5 to 10 percent.
With spheres of 100 to 300 microns in diameter, a total geometric
area of 75 cmz/cm3 is obtained. Thus, "the current density is
very low and the flow of electrolyte through the bed provides the
forced convection to support high currents. Another system
employs electrodes made of expanded metal and the turbulence
around this structure enhances the rate of deposition of metal
when solution is pumped past it. Turbulence and an increase in
the rate of deposition at a plane electrode may also be promoted
by filling the space between electrodes with a woven plastic
screen, glass beads, etc.
In another system(52) the electrolyte is introduced into a narrow
gap between two porous carbon electrodes. The bulk of the
solution (99%) is forced through the cathode where copper is
deposited out. Pre-deposited copper on the anodic electrode is
dissolved into the one percent of the electrolyte that permeates
through this electrode and a copper concentrate is produced. The
two electrodes are periodically reversed so that copper deposited
from a large volume of solution is dissolved into a small volume
of electrolyte. Copper in solution has been reduced from 670
mg/1 to 0.55 mg/1 in the cathode stream and concentrated to 44
g/1 in the anode stream. A similar system has been used for
depositing metallic impurities from strong caustic solutions
(53) .
PracticalimOgeratingi: Systems* There are no practical operating
systems in the electroplating industry, although the caustic
purification system is in use in the chlor-alkali industry,
jDemgfistratj,sn_Statas. The porous electrode system (52) is still
under development at The University of California and has been
scaled up to handle 250 gpd of copper sulfate solution.
106
-------
Water Conservation bv Carbon Adsorption
Applicability, Activated carbon has been used for the adsorption
of various materials from solution, including metal ions.
Experimental data show that up to 98 percent of chromium can be
removed from waste water (49). The treated water can be recycled
to the rinse tanks.
The process relies upon the
adsorption of metal ions on specific types of activated carbon.
In the case of Cr+6 a partial regeneration of the carbon can be
accomplished with caustic solution followed by an acid wash
treatment to remove residual caustic and condition the carbon bed
for subsequent adsorption cycles. The equipment consists of
holding tanks for the raw waste, pumps and piping to circulate
the waste through adsorption columns similar to those used for
ion-exchange.
Practical,, Operating Systems. Systems based on adsorption and
desorption are still under laboratory development and no
practical operating systems are known.
Demonstration Status. Pilot plant equipment has been operated
successfully in an electroplating plant treating chromium rinses
at a flow rate of 19 liters/min (5 gpm) at concentrations from
100 to 820 mg/1 hexavalent chromium. Adsorption was continued
until the effluent reached acceptable concentrations of
hexavalent chromium.
Water Conservation by Liquid-LiquidExtraction
ABBJticabi1it^. Liquid-liquid extraction has been used on an
experimental basis only for the extraction of hexavalent chromium
concentrate impurities in a smaller volume, which in turn will
have to be treated by other means or suitably disposed of. The
fully extracted aqueous phase may be recycled to the rinse tanks.
Water savings from 50 to 73 percent appear to be possible.
ProcessccPrinciglfs and Eqpi pment. The metal-ion pollutant is
reacted with an organic phase in acid solution, which separates
readily from the aqueous phase. Metal is subsequently stripped
from the organic phase with an alkaline solution, Hexavalent
chromium, for example, has been extracted from wastewater at pH
2 with tertiary and secondary amines dissolved in kerosene.
After the reaction of the chromium with the amine and phase
separation, the chromium is stripped with alkaline solution from
the organic phase restoring the amine to its original
composition. For liquid-liquid extraction to be feasible the
following conditions would have to be met:
107
-------
(1) The extraction of chromium should be virtually complete.
(2) Reagent recovery by stripping would be efficient.
(3) The stripping operation should produce a greatly concen-
trated solution.
(4) The treated effluent solution should be essentially free
from organic solvents.
(5) Capital and operating costs should be reasonable.
The equipment required consists basically of mechanically
agitated mixing and settling tanks, in which the phases are
intimately dispersed in one vessel agitation and then permitted
to flow by gravity to a settling vessel for separation. Holding
tanks for extraetant and stripper and circulating pumps for these
solutions as well as the purified waste water are necessary.
Equipment for liquid-liquid extraction would also include
horizontal and vertical columns, pulsed columns and centrifuges.
Practical Operating Systems. Liquid-liquid extraction systems
are not known to be operating for treatment of electroplating
wastes.
Demonstration __ Status . Experimental evidence exists indicating
that up to 99 percent of chromium can be successfully extracted
from rinse waters containing 10 to 1000 mg/1 of Cr+6. With 10
mg/1 of Cr+6 in the rinse water, the treated effluent contained
as little as 0.1 mg/1 of the ion; with 100 mg/1 in rinse water
concentration was reduced to 0.4 mg/1. Stripping was effective
as long as the amines were not allowed in contact with the
chromium for a prolonged period of time which would allow
oxidation by Cr** ions. The effluent, however, contained from
200 to 500 mg/1 of kerosene, which is undesirable.
Although chemical methods of treating electroplating waste waters
are achieving the low effluent discharges suggested in this
report, they are not improvable to the point of achieving zero
discharge of pollutants. The preceding discussion of water
conservation [ion exchange, evaporation, and reverse osmosis
(RO^ ] indicates procedures for achieving no discharge of water.
With closed- loop treatment of rinse water in separte streams from
each electroplating bath, evaporation or HO can be used to return
concentrate directly to the corresponding plating bath.
Impurities in an electroplating bath are increased in
concentration when pollutants in rinse waters as recycled and
returned to the solution. High concentrations of impurities
ultimately affect the quality of the electroplates. Thus,
108
-------
impurity removal becomes necessary. Methods for removing
impurities usually contribute pollutants that must be disposed of
by chemical treatment. For example, the removal of carbonates
from cyanide pollution by precipitation with calcium hydroxide or
by freezing involves cyanide and metals, which must be subjected
to chemical treatment. Activated carbon for removing organic
impurities should be washed before disposal as a solid and the
wash water treated to destroy cyanide and/or precipitate metals.
Spills that cannot be returned to the segregated recovery cycles
must be treated chemically to avoid pollution. These sources of
pollutants can be combined with waste water flows from alkaline
cleaners, acid dips and other preplating and post plating
solutions; from which chemicals cannot be recovered and returned
to the process. These preplating and post plating solutions are
either changed irreversibly during use or become too contaminated
for economic recovery. Replacement or makeup is unavoidable if
the solutions are to perform their proper function. Although
rinse water can be recycled, a sludge is inevitable in connection
with recovering most of the water by chemical treatment. This
operation is best performed after mixing the rinse waters from
the cleaner and acid dips.
The acid in acid dip solutions gradually becomes neutralized by
reaction with the basis metal being processed, and the
concentration of the metal increases. Ion exchange can be used
in a separate stream of waste rinse water to recycle the water to
rinsing. However, the regenerant must be disposed because it
contains the dissolved metals that are not recyclable in the acid
dipping operation. Most commonly this will be done by chemical
precipitation, after mixing with the rinse waters.
A preferred procedure (A) for eliminating discharge of pollutants
into navigable streams omits the ion exchange step and
concentrates the rinse waters to recycle some of the water and
minimize the chemical treatment load as shown in Figure 15. Wash
water from spills is fed into either the alkali or acid rinse
water holding tank, obviously dumps of concentrated cleaners and
acid dips can be trickled into the respective rinse water holding
tank. Rinse water containing post plating pollutants also can be
treated by directing it to holding tanks prior to treatment by
evaporation or RO and ultimate chemical treatment and
precipitation of heavy metal pollutants.
Another procedure (B) for recycling water to rinse tanks and
achieving no discharge of pollutants includes chemical treatment
of the combined waste from all preplating, plating and post
plating operations and separation of solids as discussed on pages
61-79, followed by further treatment of the effluent by
evaporation or reverse osmosis to recover high-quality water
suitable for rinsing. This water recovery system is used with an
RO unit at Rock Island Arsenal (Figure 12) , The concentrate from
the RO unit (or an evaporator) is evaporated to dryness and
disposed of as a granulated salt. When this method for achieving
zero discharge of pollutants into navigable streams is adopted
with no provision for recovering chemicals reusable in
109
-------
Recycle Rinse
Water
Holding Tank
for
Rinse Water
From Cleaner
h-
!_•
o
Holding Tank
for
Rinse Water
From Acid
Dip
Solid
Salt
Concentrate
Evaporate
to
Dryness
Concentrate
FIGURE 15.
FLOW CHART FOR TREATMENT OF WASTE WATER FROM CLEANER AND ACID DIP
WHEN PLATING OPERATIONS HAVE SEPARATE STREAM TREATMENT
-------
electroplating baths, costs will be greater than the costs
incurred for recycling electroplating chemicals in segregated
streams and combining preplating and post plating rinse water for
chemical treatment and subsequent evaporation or RO for water
recovery.
A possible future development may be direct treatment of the
waste water stream by evaporation or reverse osmosis without
prior precipitation of the metals. The waste water would need
adjustment to a low enough pH to preclude any precipitation which
could cause corrosion problems or membrane deterioration. The
method would have the obvious merit of reducing the cost of
chemical treatment and limiting it to that required for cyanide
destruction and chromate reduction. However, the solid residue
from evaporation may contain soluble heavy metal salts that would
require further treatment before being used as land fill.
Ill
-------
-------
SECTION
COST4_.rENERGY.,. iANp,..NQNWATE3Riii QUALITY ASPECTS
Introduction
In this section, costs associated with the degree of effluent
reduction that can be achieved by exemplary treatment methods are
discussed. Costs also are estimated for evaporation and reverse
osmosis technologies that can achieve a further improvement in
removing waste water constituents. The nonwater quality aspects
concerning disposal of solid waste and the energy impact of the
inprocess control and waste treatment technologies also are
discussed.
Treatment and Control Costs
Chemical Treatment to Achieve Low Levels of Pollutants
Best Practical Control Technology Currently Available Li rn it a t i on s
(Table lj^ Costs associated with control technology consistent
with the exemplary practice of chemical treatment averaged
S10.2U/100 sq m (1.52/1000 sq ft) for eight medium-sized and
large plants that supplied detailed cost data. The standard
deviation for this value was $6.31/100 sq m ($5.86/1000 sq ft)
indicating considerable spread from the average value. The
operating cost of waste treatment, as a percent of cost of
plating was 3,80$ with a standard deviation of 2.37%. Plating
costs were assumed to be $2.70/sq m (0.25/sq ft) for each deposit
applied, (Copper, nickel, chrome on the same part corresponds to
three deposits.) The minimum investment cost for a chemical
treatment plant is of the order of $50,000 regardless of the size
of the plating installation. For plants with a plating capacity
of 107 sq m/hr (1000 sq ft/hr), or larger, the investment cost is
estimated at approximately $150,000/100 sq m/hr ($140,000/1000 sq
ft/hr) of capacity (Figure 16) .
The control and treatment technology on which the above costs are
based will reduce the discharge of waste water constituents to
only 0.1 to 1.0 percent of the amount that would be discharged in
the absence of chemical treatment.
The costs of waste treatment in smaller plants was estimated
using a model that included chemical treatment consisting of
cyanide destruction and hexavalent chromium reduction and
precipitation and separation of metals from the combined waste
water from preplating, plating, and postplating operations.
A minimum capital investment of $50,000 was assumed for the
chemical treatment facility in any small plant. Only 2,000 hours
of operation per year (8 hg/day 5 days/week, 50 weeks/yr) was
assumed for the small plants in place of 2,625 hours per year for
medium-sized Plant 33-1, becuase many small plants confine their
operations to only one, 8-hour shift. As a result of these
Preceding pap blank
113
-------
tfi
w
_O
"o
•a
fc
o
o
c
0)
I
2.5
2.0
1.5
1.0
0.5
Square Meters Plated/Hour x I05
0.5 1.0
1.5
4
10
12
14
16
Square Feet Plated/Hour x I03
FIGURE 16
EFFECT OF SIZE OF PLATING PLANT ON
INVESTMENT COST OF WASTE-TREATMENT
FACILITY
114
-------
assumption, fixed charges and operating costs, based on area
planted, are higher for the small plants.
Table 22 shows that estimated costs for meeting the 1977 BPCTCA
effluent limitations by chemical treatment are greater for small
plants plating less than 33 sq m/hr (360 sq ft/hr) in comparison
with the costs for meeting 1977 BPCTCA limitations by larger
plants. The figures in Table 22 reflect the fixed costs for
capital investment depreciation, interest on the investment and
variable costs for chemical treatment. The variable costs for
chemical treatment were based on cost data supplied by Plant 33-
1. These variable costs at Plant 33-1 were as follows:
Chemicals $28,439/yr
Sludge disposal 5,144/yr
Labor 23,433/yr
Equipment repair 3,889/yr
Power 3,887/yr
Total $6U,792/yr
Plant 33-1 operates 2,625 hr/yr and has a plating rate of 4,560
sq ft/hr (12,000,000 sq ft/yr). The above cost is about
$5.70/100 sq m ($5.30/1000 sq ft), which is about the average
cost calculated for 6 other plants. The cost is about $2/1000
gal (assuming 2»5 gal/sq ft.) and is typical of values reported
for chemical treatment.
According to the estimates in Table 22, the costs for chemical
treatment in a small plant with 6 to 10 employees are
approximately 7 percent of the total plating costs, assuming that
plating costs are $2.70/sq m ($0.25/sq ft). In comparison, costs
for chemical treatment in a plant with 2 employees are
approximately 18 percent of the plating costs.
As noted previously, the estimates in Table 22 are based on a
capital investment of $150,000/100 sq m/hr ($1UO,000/ 1000 sq
ft/hr). Any plant capable of designing and constructing a
chemical waste treatment facility at a lower cost will have a
lower waste treatment cost per unit area plated. The eight
larger plants cited on page 122 obviously were able to reduce
their capital investment appreciably because operating costs at
these plants averaged only $10.24/100 sq m ($9.52/1000 sq ft),
which is only about one half of the estimated cost in Table 22
for small plants with 6 to 20 employees.
New Source Performance Standgrds JjSPSLa, New sources that are
required to meet the standards of performance recommended in
Table 1 have the opportunity of designing and building plants
that reduce water flow. Such a reduction can be accomplished by
installing counterflow rinsing for each preplating and
postplating operation. The capital investment cost for
installing a supplemental rinse tank for each operation in a
plant plating copper, nickel, chromium and zinc will be
approximately $20,000, The impact of this supplemental capital
115
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TABLE 22. ESTIMATED COSTS FOR SMALL ELECTROPLATING FACILITIES WITH NO WASTE TREATMENT TO MEET
EFFLUENT LIMITATIONS FOR 1977 AND 1983(a)
Treatment Costs (c)
Annual
Sales
$/yearO>)
60,000
90,000
120,000
150,000
£ 180,000
m 210,000
300,000
600,000
Number of
Employees
2
3
4
5
6
7
10
20
Chemical Treatment
for BPCTCA (1977)
$7100 sq m
46.1
32.6
25.8
21.8
19.3
19.3
19,3
19.3
$/1000 sq ft
42.8
30.3
24.0
20.3
17.9
17.9
17.9
17.9
Chemical Treatment
for NSPS . .
$/100 sq m
62.2
43.4
33.9
28.3
24.6
24.6
24.6
24.6
$/1000 sq ft
57.8
40.3
31.5
26.3
22.9
22.9
22,9
22.9
Zero Discharge
BATEA (1983)
$/100 sq m
75.6
53.3
42.2
35.9
31.6
30.7
28.9
27.0
$/1000 sq ft
70.3
49.5
39.2
33.4
29.4
28.5
26.9
25.1
(a) Based on minimum investment of $50,000 for small chemical treatment facility.
(b) Based on manual electroplating operation and $10,000/yr salary per employee and annual sales of
$30,000 per employee; 60 sq ft/hr per employee; approximately 330 amperes per employee.
(c) Treatment cost divided by 2.5 is percent of plating costs based on $0,25/sq ft plated.
-------
investment on waste treatment costs for small companies is
reflected in Table 22, Estimated costs for a 6 to 20 employee
plant plating 33 to 167 sq m/hr (360 to 800 sq ft/hr) amount to
approximately 9 -percent of the total plating costs, assuming that
plating costs are approximately $2»7Q/sq m ($0.25/sq ft).
Large companies plating more tha 167 sq m/hr (1800 sq ft/hr) will
incur costs of no more than $19.30/100 sq m ($17.9/1000 sq ft) to
meet new source performance standards. The level of costs for
meeting NSPS might be lower if investment costs for chemical
treatment are lower than $150,000/100 sq m/hr ($110,000/1000 sq
ft/hr),
No Discharge of Pollutants
The elimination of waste water discharge pollutants can be
accomplished by water recovery by evaporation-condensation or
reverse osmosis in combination with chemical treatment and
filtration for acid/alkali waste. Ion exchange is useful for
waste water conservation, but is not practical for eliminating
waste waller constituents in the end-of-process, point source
discharge. The preferred,, mode of operation is to conserve all
plating bath chemicals and return them to the plating bath, and
concentrate all other chemicals (from preplate and postplate
operations) for chemical treatment and disposal in a solid state.
The cost for eliminating waste water pollution using evaporation
(and no chemical treatment) in a plant with a plating capacity of
370 sq m/hr ($1000 sq ft/hr) is estimated to range from $5.40 to
$17.20/100 sq m ($5.00 to $16.00/100f sq ft) or 2 to 6.5 percent
of the plating costs. The lower figure is associated with the
use of a vapor compression system for combined preplating and
postplating waste and individual single stage evaporators for
recovering plating solution from rinse water following plating
operations. The higher figure is associated with single effect
units employing steam and cooling water for each preplating,
plating, and postplating operation. The capital investment
estimates for these evaporation systems are $68,659 and
$164,000/100 sq m ($63,810 and $153,000/1000 sq ft) for the vapor
compression and single effect evaporation systeirf, respectively.
'j,
Costs incurred by a large plant for eliminating waste water
pollutants by chemical treatment followed by reverse osmosis are
estimated to be of the order of $8.60/100 sq m ($8.00/1000 sq ft)
or less, equivalent to about 3 percent of the plating cost. The
capital investment estimate for this system is $110,000/100 sq
m/hr ($102,100/1000 sq ft/hr). Waste water pollution will be
eliminated in this case but there will be a discharge of small
amounts of both soluble and insoluble solid wastes.
The incremental cost for achieving zero discharge of pollutants
by 1983 by a large facility plating at least 370 sq m/hr (4000 sq
ft/hr), which is now equipped for meeting 1977 new source
standards or 1977 existing source limitations via chemical
117
-------
treatment is estimated to be $3.39/100 sq m ($3.15/1000 sq ft).
This incremental cost assumes that effluent osmosis to recover
water and that concentrate from the RO unit will be evaporated to
a granulated salt.
Estimated costs for eliminating waste water pollution from small
plants that recover no plating solution via evaporation or
reverse osmosis are much higher than the costs for achieving zero
discharge of pollutants in plants that use evaporation or reverse
osmosis to recover plating solution draged into rinse water
tanks. The estimates in Table 22 show the higher costs
associated with chemical treatment of combined waste water from
all preplating, plating, and postplating operations plus reverse
osmosis (to recover water) plus evaporation of the concentrate to
granulated salt. These estimates vary with the size of the
plating facility. Costs increase appreciably as plant size is
reduced from 20 to 2 employees. At the 20 employee level, costs
for achieving zero discharge of pollutants with no recovery of
plating solution amount to approximately 10 percent of the total
plating costs (assuming plating costs are approximately $2.70/sq
m ($0.25/sq ft)). In comparison a plant with only two employees
would entail costs equivalent to about 28 percent of plating
costs to achieve the same standard of performance.
The incremental cost for achieving zero discharge of pollutants
by 1983 for a small facility plating no more than 167 sq m/hr
(1800 sq ft/hr)» which is initially equipped for meeting 1977 new
source standards via chemical treatment can be estimated from
data in Table 22. This increment will vary from $13.40/100 sq m
($12.45/100 sq ft) for a 2 employee plant to $2.40/100 sq m
($2.34/1000 sq ft) for a 20 employee plant.
CostEffectiveness and Treating Procedures
From an analysis of untreated rinse water and effluent in Plant
33-1 which corresponds to a medium-sized plant (50,000 amperes)
with 38 employees, it was possible to calculate the amount of
copper, chromium, nickel, zinc, and cyanide removed from the
rinse water and determine the amount discharged with the
effluent. The volume of discharge for various rinse-tank
arrangements and the costs associated with these arrangements
were also known. The costs of applying increasingly effective
treatment techniques to Plant 33-1 were estimated for the
following systems:
(1) A single rinse tank for each rinsing operation; no
wastewater treatment
(2) A single rinse tank for each rinsing operation; chemical
treatment
(3) Two series rinses for each rinsing operation; chemical
treatment
118
-------
Three counterflow rinses for each rinsing operation;
chemical treatment
(5) Single-stage evaporation for each process bath plus 3
counterflow rinses, cleaners and acid dips included,
which requires a total of 21 evaporators. All rinse
water would be recycled and plating process rinse water
would be returned to the plating bath. Thus, no
chemical treatment was included
(6) A single-stage evaporator for each process bath and
counterflow rinse, except for acid and alkaline
preplating and postplating rinses. A large vapor
compression unit was assumed for the acid-alkali and
postplating stream. Effluent volume reduced to
approximately 37.8 Ipd (10 gpd). No provision was made
for evaporating this very small volume to dryness.
(7) Process lines as they now exist in Plant 33-1. Chemical
treatment is used, followed by reverse osmosis on the
effluent from the chemical treatment. No provision was
made for evaporating the small volume of concentrate
from the RO unit.
From these data sources, a cost effectiveness curve was plotted,
as shown in Figure 17. The volume of water required for rinsing
in single rinse tanks is so large that no precipitation occurs
during chemical treatment and the weight of discharged water
constituents is not affected by the treatment. The lowest cost
on the curve is that now incurred by Plant 33-1 using their
present system. The options listed for eliminating discharge of
wastewater constituents are associated with costs ranging from
$5.40 to $17.20/100 sq m ($5.00 to $16.00/1,000 sq ft).
Nonwaiver Qua 1 itv Aspects
Energy Requirements
C^emical^Treatment» The electric power used for plating consumes
about"" 0.06 percent of the nation's electrical energy (1.7 x 1012
kilowatt hours). The power required for chemical treatment is
approximately 3.2 percent of the power needed for plating, based
on data developed from a sample of eight plants with reliable
records.
No Discharge^ of Pollutants. Exclusive use of double effect
evaporators for reducing rinse water volume requires steam at a
cost that can be one to four times the cost of power for plating,
depending upon the degree of rinse water reduction achieved. Use
of vapor compression units in part or in whole will reduce the
cost of energy requirements to about the same as the cost of
electrical energy for electroplating or probably less, and
eliminate discharge of pollutants when combined with chemical
treatment. Reverse osmosis will achieve the same effluent
119
-------
JsJ
O
O
o
o
o
TJ
u>
o
c
'o
*~
33
Q.
O
50
40
30
20
10
-Nr
Single stage
evaporation
Reverse osmosis
1 Vapor compressor
evaporator
Waste Water Constituents, Ib/IOOO sq ft/hr
|0-
Three
counterflow
! rinses
Plant 33-1
Two series
rinses
|0o
10'
o Single rinse
Chemical treatment
Single rinse
No chemical treatment -
10'
Waste Water Constituents, kg/ 1000 sq m/hr
500
400
E
cr
M3
O
o
g
300 £
o
o
O
200 o<
a.
o
100
FIGURE 17 . COST EFFECTIVENESS OF TREATMENTS AND IN-PROCESS
WATER CONSERVATION TECHNIQUES
-------
limitation (when combined with chemical treatment} using 27
percent of the power required for electroplating.
Solids Disposal
The cost of lagooning sludge from a clarifier after chemical
treatment has not been considered, because the method is finding
less and less favor as a means of disposal. The volume generated
by the domestic plat ing industry is estimated to be about 200,000
cu yd/yr.
For ecological reasons, an alternative to land filling should be
sought, such as recovering metal values, if the effluent
guidelines and standards of performance recommended in this
document are adopted. All solids from the waste treatment should
be recycled within the industrial complex.
121
-------
-------
an electroplating process. All other processes and operations
defined by SIC 3471 that are not part of processes containing at
least one electroplating operation are excluded from this
category.
The identification of Best Practicable Control Technology
Currently Available and recommended effluent limitations
presented in this section cover the subcategory of rack and
barrel electroplating of copper, nickel, chromium, and zinc.
Effluent limitations are not specified as yet for all metals, all
electroplating operations, or all metal finishing processes.
However, the control and treatment technology identified is
broadly applicable in three other areas: (1) electroplating
operations other than rack and barrel; (2) electroplating of
metals other than copper, nickel, chromium, and zinc; and (3)
other metal finishing processes than electroplating yet to be
considered. Recommended effluent limitations applicable to these
other subcategories might require a greater or lesser degree of
effluent reduction.
Identification of_Best Practica.blftpContrQl
TeghnQl9gv_Currgntly_Available
Best practicable Control Technology Currently Available
subcategory of rack and barrel electroplating of copper, nickel,
chromium, and zinc is the use of chemical methods of treatment of
wastewater at the end of the process combined with the best
practical in-process control technology to conserve rinse water
and reduce the amount of treated wastewater discharged.
Chemical treatment methods are exemplified by destruction of
cyanide by oxidation, reduction of hexavalent chromium to the
trivalent form, neutralization and coprecipitation of metals as
hydroxides or hydrated oxides with settling and clarification to
remove suspended solids prior to discharge. The above technology
has been widely practiced by many plants for over 25 years.
However, the above technology cannot achieve zero discharge of
metals because of finite solubility of the metals. In addition,
it is not practicable to achieve 100 percent clarification and
some small amount of metal is contained in the suspended solids.
By optimum choice of pH and efficient clarification, the heavy
metal pollutional load may be less than 1 mg of total metal
(soluble plus insoluble) discharged for each kilogram of metal
electroplated on a basis materials. This degree of pollution
reduction can be achieved if the concentrations of all metals is
high in the raw waste.
Because of the variety of electroplating processes and metals
possible to a single plant and the high cost of in-plant
segregation of all waste streams according to metal,
coprecipitation of metals is the general practice. There is a
different optimum pH of the separate precipitation of each metal
as a hydroxide. The pH chosen for the co-precipitation of these
metals must be a compromise and will not effect as great a
removal as segregated precipitation.
124
-------
SECTION IX
BEST PRACTICABLE CONTROL^ TECHNOLOGY^ CURRENTLY
AVAILA.BLEA_GUIDEI.INESf__AND_LIiMITATIOlg
introduction
The effluent limitations which must be achieved July 1, 1977, are
to specify the degree of effluent reduction attainable through
the application of the Best Practicable Control Technology
Currently Available. Best Practicable Control Technology
Currently Available is generally based upon the average of the
best existing performance by plants of various sizes, ages, and
unit processes within the industrial category and/or subcategory.
Consideration was also given to:
(a) the total cost of application of technology
in relation to the effluent reduction benefits
to be achieved from such application;
(b) the size and age of equipment and facilities
involved;
(c) the processes employed;
(d) the engineering aspects of the application of
various types of control techniques;
(e) process changes;
(f) non-water quality environmental impact
(including energy requirements) .
The Best Practicable Control Technology Currently Available
emphasizes treatment facilities at the end of a manufacturing
process but includes the control technologies within the process
itself when the latter are considered to be normal practice
within an industry.
A further consideration is the degree of economic and engineering
reliability which must be established for the technology to be
"currently available.11 Demonstration projects, pilot plants and
general use, must show that there exists a high degree of
confidence in the engineering and economic practicability of the
technology at the time of commencement of construction or
installation of the control facilities.
§ubcateg. ory Covered
The pertinent industry category is the electroplating industry
which is part of the metal finishing industry. This category
includes plants using electroplating processes as defined by SIC
3471 (1972) and includes all electroplating processes and their
associated pretreatment and post -treatment operations if used in
Preceding page blank
123
-------
There are several advanced plating bath recovery methods
available for closing up the rinse water cycle on individual
plating operations. Among these methods are evaporation, ion
exchange, reverse osmosis, and countercurrent rinsing.
Application of these techniques to pretreatment and posttreatment
operations is not known. The corresponding rinse waters plus
concentrated solution dumps and floor spills may contain one or
all of the pertinent metals in amounts sufficient to require
chemical treatment. Thus, chemical treatment of at least the
typical acid/alkali stream from pretreatment and posttreatment
operations represents the best practicable control technology
currently available to achieve the effluent limitations
recommended.
Having identified the technology for end-of-process treatment and
recognizing the technical and practical limitations on removal of
metals by this technology (metal solubility and clarification
efficiency), further reduction in the quantity of metal
pollutants discharged must be achieved by reduction in the volume
of treated water discharged. There are many in-process controls
designed to reduce the volume of wastewater which principally
results from rinsing. Controls such as reclaim tanks and still
rinses designed to to minimize and reclaim dragout of
concentrated plating solution can be considered normal practice
within the industry. Evaporation losses are made up with the
reclaimed solution, Dragout reclaimed does not contribute to the
raw waste load normally discharged from remaining rinses.
Practicing dragout reclaim is economically wise because it
reduces the cost for make up and treatment chemicals. Reduction
of dragout leads to reduction in water requirements for rinsing.
Further reduction in rinse water use can be achieved by multiple
tank countercurrent rinsing. Unless the rinse water can be used
to make up evaporation losses of the bath, there is little
reduction in treatment chemical cost and no economic incentive to
add more rinse tanks purely for water conservation. However, the
use of advanced recovery techniques (evaporation, ion exchange,
and reverse osmosis) which concentrate the rinse water
sufficiently to allow reclaim of the valuable plating solution
provides the economic incentive to use this technology and
justifies the cost of recovery equipment plus the cost of
installing multitank countercurrent rinsing. However, it should
be recognized that the major water reduction occurs because of
the installation and use of multitank countercurrent rinsing.
The additional reduction in volume of wastewater by recovery of
all the rinse water following a plating operation in lieu of
chemical treatment usually has limited impact on the total water
use in the plant. This is because the volume of rinse waters
from pretreatment and posttreatment operations (e.g., the
acid/alkali wastewater stream) is often several times larger than
the volume of rinses from plating operations.
In the past there has been little economic incentive to reduce
water use for rinsing after pretreatment and posttreatment
operations. For one reason, the chemicals used in these
125
-------
solutions are not expensive compared to plating solution
chemicals and thus they are not purified for reuse. These
concentrated solutions are dumped at frequent intervals and there
is usually little concern for reducing dragout since the dragout
reduces the rate of buildup of impurities and extends the life of
the concentrated solution so that less frequent dumping is
required. Thus, for pretreatment and posttreatment solutions
that are dumped frequently (e.g., once a week), dragout does not
influence the quantity of material in the wastewater requiring
treatment. However, dragout from these solutions does influence
the amount of water required for adequate rinsing.
While sufficient economic incentive is presently lacking to
achieve reduction in the volume of the rinse water from pre- and
post-treatment operations, there is an opportunity for significant
reduction in pollution. The above factors are taken into account
in recommending the effluent limitations. Even in plants
currently achieving good waste-treatment results, there are
further opportunities for reduction in volume of effluent
discharged provided there is an economic incentive related to
achieving pollution reduction.
Rationale^for^Selectingthe_BestLPracticableControl
Technology JgurrentlyAvailable
General Approach
In determining what constitutes the Best Practicable Control
Technology Currently Available, it was necessary to establish the
waste management techniques that can be considered normal
practice within the electroplating industry. Then, waste-
management techniques based on advanced technology currently
available for in-process control and end-of-process treatment
were evaluated to determine what further reduction in pollution
might be achieved considering all the important factors that
would influence the determination of best practicable and
currently available technology.
WasteiiManagerTtent_Technigues_Con3i.dered
Normal practice in the Electroplating Industry
For that portion of the electroplating industry that discharges
to navigable waters it is estimated that a large proportion are
currently using chemical treatment for end-of-process pollution
reduction. Some of these waste-treatment facilities have been in
operation for over 25 years with a continual upgrading of
performance to achieve greater pollution abatement. Because of
the potentially toxic nature of the chemicals used in the
electroplating industry, there is a relatively high degree of
sophistication in its water pollution abatement practices. For
example, the accidental release of concentrated solutions without
treatment to navigable waters is believed to be a rare occurrence
today. This is because adequate safety features are incorporated
in the design of end-of-process waste treatment facilities in
126
-------
conjunction with good housekeeping within the electroplating
facility. This example and other waste management techniques
were considered as examples of normal practice within the
electroplating industry in determining the Best Practicable
Control Technology Currently Available. Other examples of normal
practice include:
(1) Manufacturing process controls to minimize dragout from
concentrated plating solutions
(a) proper racking of parts for eary drainage
(b) slow withdrawal of parts from the solution
(c) adequate drip time or dwell time over the plating
tank
(d) use of drip collection devices.
(2) Effective use of water to reduce the volume of effluents
(a) use of rinse water for makeup of evaporation losses
from plating solutions
(b) use of cooling water for noncritical rinses after
cleaning
(e) use of treated wastewater for preparing solutions
of waste- treatment chemicals.
(3) Recovery and/or reuse of wastewater constituents
(a) use of reclaim tanks after plating operations to
recover concentrated solutions for return to the
plating tank to make up evaporation losses
(b) reduction in wastewater volume by the use of at
least two series flow rinse tanks after each
plating operation with return of as much rinse
water as possible to the plating tank.
Other waste-management techniques currently in use in one or more
plants were evaluated on the basis of reduction in the quantity
of pollution in the effluent discharged.
Reduction Based .ojn
.....
Existing Performance by Plants of Various ,
Various Control and Treatment Technology
Identification of Best Waste Treatment Facilities
There are about 20,000 facilities for electroplating and metal
finishing in the United States and identification of the best
plants within the short period of this study required a rational
screening approach as follows. The initial effort was directed
toward identifying those companies which satisfied two criteria:
1. are engaged in rack and barrel plating of copper,
nickel, chromium and/or zinc
2. are achieving good waste treatment.
127
-------
The 309 companies were identified based on referrals by cognizant
people associated with the industry (EPA regional
representatives, state pollution control authorities, trade
associations, equipment suppliers) and review of permit
applications were distributed geographically as shown in Table
23. About 90 percent of the companies were in the three
principal regions expected to have high concentrations of
electroplating industry: 38 percent in the Northeast
(principally !PA Regions I, II and III; 28 percent in the Midwest
(EPA Region V): 25 percent in the Southeast (Region IV)).
Of these leads, the 129 companies initially contacted by
telephone were primarily in the principal electroplating regions
-------
TABLE 23. GEOGRAPHICAL DISTRIBUTION OF GOOD ELECTROPLATING
WASTE TREATMENT FACILITIES BASED ON INITIAL
REFERRALS, COMPANIES CONTACTED FOR INFORMATION,
AND REPRESENTATIVE FACILITIES EVALUATED IN
DETAIL
Area
Referral
Contact
Evaluated
EPA Region I
Connecticut
Massachusetts
New Hampshire
Rhode Island
Maine
Vermont
EPA Region II
Delaware
New Jersey
New York
EPA Region III
Maryland
Pennsylvania
Virginia
West Virginia
EPA Region IV
Alabama
Florida
Georgia
Kentucky
Mississippi
North Carolina
South Carolina
Tennessee
32
26
2
1
2
3
3
11
18
7
7
3
2
16
14
5
4
5
15
11
8
12
2
2
1
2
13
4
4
7
4
'2
2
1
1
7
3
2
1
2
4
2
1
2
1
2
(Continued)
129
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TABLE 23 ,GEOGRAPHICAL DISTRIBUTION OF GPOD ELECTROPLATING
WASTE TREATMENT FACILITIES BASED' ON ,INITIAL
REFERRALSi- COMPANIES CONTACTED FOR INFORMATION,
AND REPRESENTATIVE FACILITIES EVALUATED IN
DETAIL
(Continued)
Area
EPA Region VI
Arkansas
EPA Region VII
Iowa
Kansas
Missouri
Nebraska
EPA Region VIII
Utah
EPA Region IX
California
EPA Region X
Washington
Referral
Contact
Evaluated
EPA Region V
Illinois
Indiana
Michigan
Minnesota
Ohio
Wisconsin
22
14
18
4
21
8
10
6
13
• 1
19
2
3
6
7
1
11
10
1
6
1
1
3
1
2
1
4
1
1
1
130
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TABLE 23,GEOGRAPHICAL DISTRIBUTION OP GOOD ELECTROPLATING
WASTE TREATMENT FACILITIES BASED ON INITIAL
REFERRALS, COMPANIES CONTACTED FOR INFORMATION,
AND REPRESENTATIVE FACILITIES EVALUATED IN
DETAIL
(Continued)
Area
EPA Region V
Illinois
Indiana
Michigan
Minnesota
Ohio
Wisconsin
Referral
22
14
18
4
21
8
Contact
10
6
13
- 1
19
2
Evaluated
3
6
7
1
11
EPA Region VI
Arkansas 44 3
EPA Region VII
Iowa 10 2 1
Kansas 1 ' 1
Missouri 64 1
Nebraska 11 1
EPA Region VIII
Utah 1
EPA Region IX
California 3 1
EPA Region X
Washington 1 1
131
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TABLE 24. CLASSIFICATION BY SIZE, TYPE OF FACILITY,
AND EFFLUENT DISCHARGE FOR 53 ELECTRO-
PLATING FACILITIES SELECTED FOR
EVALUATION
Relative
Size
Very large
Large
Medium
Small
Very small
Captive
Amperes Munic-
Installed ipal
over 200,000
50,000-200,000 7
10,000-50,000 4
1,000-10,000 7
less than 1,000
Stream
1
2
11
6
1
Job
Munic-
ipal Stream
1
.1 2
5 3
1 1
__ —
132
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Classification of 53-Plant Sample
Table 25 shows the scope of coverage for the 53 plants in terms
of the mix of possible plating operations and variety of control
and treatment technologies. Most plants (32) are equipped for
decorative plating of copper-nickel-chromium and of these about
half (11) also plate zinc. About 75 percent of the plants in the
sample that plate zinc also use a subsequent chromate conversion.
The remaining 21 plants provide most of the expected process
combinations of copper, nickel, chromium and/or zinc plating that
might be found in the industry. The 53 plants in the industry
sample include the variety of control and treatment combinations
to be found. Most plants (38) used some type of chemical
treatment such as continuous (C) , batch (B) , and/or integrated
(I) to treat the metals and cyanide associated with the plating
operation. A few plants use electrolytic treatment (L) and one
uses reclaim tanks for recovery (R). The other 15 plants
included examples of a variety of advanced in-process controls
combination of evaporation (E)f ion exchange (D) and reverse
osmosis (O), Most of the plants used end-of-pipe chemical
treatment (continuous or batch) for at least the acid/alkali
wastewater stream.
The classification of the 53 plants by size (based on amperes),
number of employees in plating for all shifts and waste-treatment
method is shown in Table 26. Figure 18 shows that more than half
of these plants had fewer than 20 employees per shift.
of the 53 plants, 26 were visited for on-site inspection and
verification of information. The data on rated or installed
current capacity are shown in Table 27, Figure 19 shows the same
data for total installed current capacity and indicates that 50
percent of the plants had less than 18,000 amperes. The normal
use of installed current capacity was 67 percent based on the 23-
plant average of the fraction of total rated capacity used shown
in Table 27. Thus, it was estimated that 50 percent of the
plants used less than 12,000 amperes.
Figure 20 shows the relation of installed rectifier capacity to
number of employees per shift in electroplating for the 53-plant
sample. The average value calculated is about 1000 amperes
installed/ employee. Based on an estimated typical 65 percent
use of installed capacity, the average value would be 650 amperes
used/employee per shift. The large amperage per employee for
automatic plating machines (over 5000 amperes/employee) would be
expected to result in considerable spread in the data. Thus,
number of employees is not a definitive indicator of plant size
in terms of pollutional potential. Amperes as related area
plated is a more definitive measure of plant size and raw waste
load,
Waste Treatment Results
Table 28 shows the treated effluent data and plant effluent
discharge rate (average hourly rate in 1/hr). Figure 21 shows
133
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TABLE 25-CLASSIFICATION OF 53 FACILITIES EVALUATED
BY MIX OF PLATING OPERATIONS AND TYPE OF
WASTE TREATMENT AND IN-PROCESS CONTROLS
Waste
Treatment (a)
and Control Cu Ni
C
B 1
CB
GBR
LC
I
1C
IB
IR
El
EC
EB
EDC
EDB
E
D
OB
QIC
Metals Electroplated
Cu
Cu Cu Ni Cu Ni
Cu Cu Cu N± NI Cr Ni Ni Cr Ni Cr
Cr Zn Ni Cr Zn Cr Zn Zn Cr Zn Zn Zn Zn Totals
2 161 6 16
111 1 11 7
3 3
1 1
2 2
1 12 15
2 2
1 1
1 1
2 13
1 1
11 2
1 1
1 1
2 13
2 2
1 1
1 1
Totals 01262023 01 18 310 14
(a) See Footnote (e) Table 25 for definition of symbols,
134
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TABLE 26
SOURCE OF INFORMATION AND CLASSIFICATION BY
SIZE AND WASTE-TREATMENT KETHOD
Size o!. Facility
Company
Code No. {*'
1-16
3-1
3-3
3-4
6-3
6-12
6-29
8-4
8-5
11-8
11-13
11-22
12-3
12-5
12-6
12-8
12-9
12-12
13-2
15-1
19-2
19-3
20-1
20-6
20-7
20-10
20-13
20-15
20-17
21-3
23-3
25-1
28-9
28-11
30-1
30-5
30-7
30-8
33-1
33-2
33-3F
33-3U
33-6
33-8
33-9
33-11
33-15
33-20
33-21
36-1
36-2
40-4
43-1
Reference^)
S
13
13, I
11
S, 12
S, 13
32
S
S
S, 13, L
S
33, 1
15
S
S
S
S
S
L
13
18
1, 21
S
S
S
L, 18
5, 17, i
5
5
S
7, 11
7, S
S
2
14
2
19
19
16, 5, S
S
13
13
17, L
5
S
S
S
S
5
L
32
5
S
Data
Obtained (c)
T
P
P
P
P
P
T
T
T
f
1
P
P
T
T
P
T
T
T
f
T
P
P
T
P
T
P
T
T
T
T
T
T
f
P
I
T
P
P
f
P
P
P
P
P
P
P
P
T
P
P
.T
T
Employees
in Plating
10
19
31
40
6
54
20
12
50
165
18
.-
90
25
120
100
25
70
20
6
70
30
7
80
25
250
6-10
13
50
16
200
69
15
25
52
30
15
24
38
10
1
5
100
3
16
12
20
12
18
25
13
40
2
Relative
M
M
M
M
S
M
S
S
S
I,
M
L
M
M
Vt
i
M
L
M
S
M
M
S
L
M
L
M
S
L
S
£
L
M
L
M
M
M
M
I.
S
S
S
M
VS
S
M
VL
S
L
K
S
M
S
Classification^6'
c/s/eec-cc
C/S/--BEE-
C/S/-IEI-B
C/S/EB--BB
C/S/BII— B
C/M/ENCEEN
J/S/CCICIC
C/M/CCC-CC
C/1./CCC-CC
J/S/CCSECC
J/S/CCC-CC
C/M/000-BC
J/M/NEENRC
J/M/CCCCAC
J/S/DDE-BB
C/M/CCCCCC
C/S/IRI-IC
C/M/— EE-
C/M/COI-CC
C/M/— EE-
J/S/LCLtLC
J/S/--I— C
c/s/c-cccc
C/S/CCB-BC
C/S/CCBCBC
C/M/- II— C
c/s/icmc
C/K/-BB--B
c/s/cccccc
C/S/BBBBBB
J/M/CCC-CC
C/M/CCCCCC
J/1/-B--BB
C/M/CCCCCC
J/M/iCIALC
C/S/IIIIIC
e/s/m-ie
C/M/--SBBB
J/S/CCCCCC
C/S/BNN-NB
C/M/--IEEC
C/M/ —I EEC
J/M/CCC— C
C/S/--B— B
J/M/NDD-NC
C/M/C-CCCC
C/S/CCB-BC
C/M/CCCCCC
C/M/— CCCC
C/S/BBBBBB
C/M/INI-IB
C/S/TOD--C
C/S/RCRBBB
Footnotes appear on the following page-
135
-------
FOOTNOTES FOR TABLE 26
(a) Company identification by number for this report.
(b) Source of lead to company.
(c) Information from telephone call (T) or first-round
visit (P).
(d) Relative size based on total installed rectifier
capacity in amperes for plating:
VL = very large, >200,000 amperes
L = large, 50,000 to 200,000 amperes
M = medium, 10,000 to 50,000 amperes
S = small, 1,000 to 10,000 amperes
VS = very small, >1,000 amperes.
(e) Classification by type of facility (1st letter)t
J = job shop or independent
C = captive plating facility,
where the treated effluent is discharged,
S = stream (or storm sewer to stream)
M = municipal sanitary treatment system,
L = liquid effluent disposed of on land
and the following coded waste treatment or in-process
control used for each constituent of the final effluent
considered in the order; copper, nickel, chromium, zinc,
cyanide, acid/alkali:
A = adsorption
B = batch chemical treatment
C = continuous chemical treatment
D = ion exchange
E = evaporation
I = integrated
L = electrolytic
N = no treatment beyond pH adjustment
0 = reverse osmosis
R = reclaim rinsing techniques.
136
-------
TABLE
27
SIZE OF PLATING OPERATIONS (RATED AND USED)
Company
Code Bo.
1-16
3-1
3-3
3-4
6-3
6-12
6-29
8-4
8-5
11-8
11-13
11-22
12-3
12-5
12-6
12-8
12-9
12-12
13-2
15-1
19-2
19-3*
20-1
20-6
20-7
20-10
20-13
20-15
20-17
21-3
23-3
25-1
28-9
28-11
30-1
30-5
30-7
30-8
33-1
33-2
33-3F
33-3U
33-6
33-8*
33-9
33-11
33-15
33-20
33-21
36-1
36-2
40-4
43-1
Fraction of Rated
Caoncltv Dsed
Cu
1,500
800
5,000
60D
1,500
1,000
8,150
3,000
500
600
4,000
80,000
6,150
1,000
6,000
2,000
300
13,000
5,000
1,400
27,000
750
20,000
2,650
35,100
6,750
3,300
2,000
3,000
400
7,000
1,000
3,000
63,000
3,000
4,500
250
8,000
1,500
Hi
9,000
10,000
12,000
2,500
5,000
1,500
200
2,300
25,150
8,000
1,000
17,000
2,000
120,000
9,250
16,000
5,000
11,000
23,000
20,000
45,000
4,000
8,650
43,500
600
10,000
3,000
6,000
62,000
8,000
4,000
10,000
23,000
350
8,500
4,000
273,000
200
4,500
1,500
8,100
3,000
Cr
6,000
25,000
3,000
3,000
1,500
1,000
23,150
8,000
72,000
8,000
8,000
63,000
15,600
16,000
4,000
2,000
44,250
16,000
7,500
30,000
3,000
250
50,000
750
10,000
20,000
25,000
6,000
1,500
8,000
8,500
10,000
250'
4,500
118,000
20,000
1,500
10,000
1,500
Zn
10,000
5,825
20,000
1,000
27,150
10,000
32,500
133,000
6,000
9,000
3,200
2,500
9,000
35,000
48,650
12,500
450
1,200
15,000
15,250
7,000
7,000
12,000
3,000
32,600
6,000
1,500
Total
16,500
10,000
40,825
12,800
5,500
35, 000 («0
6,100
3,200
8 160^'
94,600
26,100
7,500
Cu 81
0,8 0.8
0.3 0.8
0.04 0.05
0.3 0.6
0.4
1.0 0.8
0.3 0.4
1.0 0.5
1.0 1.0
0.8 0.9
0.5 0.6
0.4 0.4
0.2 0.2
0.7 0.7
0.4 0.4
1.0 0.3
0.9 0.9
0.1
Cr
1.0
0.2
0.5
0.5
0.9
0.3
1.0
1.0
1.0
0.7
0.9
0.7
0.5
0.7
0.8
0.2
0.3
0.9
0.4
Zn
0.7
0.5
0.3
1.0
0.5
0.8
1.0
0.8
1.0
0.3
0.7
0.8
0.8
0.6
0.9
0.4
Total
0.9
0.7
0.1
0.5
0.6
0.9
0.4
0.8
0.8
1.0
0.9
0.7
1.0
0.6
0.5
0.8
0.5
0.7
0.6
0.6
0.3
0,9
0,2
Footnotes appear on the following page.
137
-------
FOOTNOTES FOR TABLE
27
(a) Includes an additional 5,000 amperes for C<3,
(b) Includes an additional 1,000 amperes for Cd; 2,825 amperes for Ag; 35 amperes for An,
(c) Includes an additional 11,000 amperes for Cd,
(d) Includes an additional 100 amperes for Cd and 100 amperes for Sa.
(e) Includes an additional 5,700 amperes for Ag and 10,000 araperes for Sn,
(f) Includes an additional 300 amperes for Cd and 200 amperes for Ag,
(g) Includes an additional 1000 amperes for anodizing.
(h) Includes an additional 400 ampere* for Cd,
138
-------
IftBLE gg IDEATED EFFtUENT DATA
Coiapstiy
Code
80.
1-16
3-1
3-3
3-4
6-3
6-12
6-29
8-4
8-5
11-8
11-13
11-22
12-3
X2-5
12-6
12-8
12-9
12-12
13-2
15-1
19-2
19-3
20-1
20-6
20-7
20-10
20-13
20-15
20-17
21-3
23-3
25-1
28-9
28-11
30-1
30-5
30-?
30-8
33-1
33-2
33-3F
33-311
33-6
33-8
33-9
33-11
33-15
33-20
33-21
36-1
36-2
40-4
43-1
Treated Effluent.
Classification TSS
c/s/ccc-ee
C/S/--BEE-
C/S/-IEI-B
C/S/EB--BB
C/S/BII--B 3.4
C/M/ENCEEH
J/S/CCICIC
C/K/CCC-CC
C/t/eCC-eC
J/S/CCDSCC
J/S/CCC-CC
C/M/000-BC
J/M/BEEHSC
J/M/CCCC&C
J/S/DDE-BB
C/M/CCeCCC
C/S/I8I-IC
C/M/ «B-
C/M/COI-CC
C/M/ El-
J/S/lCUiC
J/S/— I— C
C/S/C-CCCC 13
C/S/CCB-BC
C/S/CCBCBC 25
C/H/-II--C
C/S/ICIIIC
C/M/-BB— S
C/S/CCCCCC 21
C/S/BBBBBB
J/M/CCC-CC
C/M/CCCCCC
J/L/-B— BB
C/H/CCCCCC 15
J/M/LCLUX:
C/S/1IIIIC
C/S/III-IC
C/W/— NBBB
J/S/CCCCCC
C/S/B8K-UB 9.5
C/M/--IEEC
C/H/--IEEC
J/M/CCC— C 8.5
C/S/--B--B
J/H/HDD-NC 9.5
C/M/C-CCCC
C/S/CCB-BC 20
C/M/CCCCCC
C/M/— CCCC 106
C/S/BBBBBB
C/M/INI-IB
C/S/DTO-- C
C/S/RCRBBB
Cu
0.5
0.018
0.08
0.08
0.53
0.1
0.03
0.1
0,3
<0.5
2.4
1.0
0.7
<1.0
3
0.15
0.18
0.096.
<0.1
<0.1
0,41
0.2
1.75
<0.07
<10,0
0,41
0.2
<0.2
<3.5
0.2
1.47
<0.1
0.13
3.1
0.2
0.21
0.12
<0.0i
0.16
<2
0.29
Nl
1.0
0,002
0.48
0.6
19.6
0.6
0.06
0.16
0.00
1.5
2.2
1.0
0.2
<1.0
2.5
<0.20
0.39
<0.7
2
0.3
<1.0
0.48
0.25
0,8
0.5
7.0
<0,2
0.3
1,0
<0.05
1.6
0.42
0.3
<0.01
7.5
<5
0.35
Crw
0.0
0,24
0.01
<0.05
0.3
0.05
0.01
<0,01
0.1
1.0
0.05
0.03
0.40
0.03
0.16
<0.0i
0.05
0.15
0.01
0.045
0.06
<0.015
<0,S
0.38
0,6
0.04
0.195
0.04
0.03
ma/1
Cr?
1.5
0.05
0,16
0.14
2.75
0.28
<1,0
0.02
1.7
1.5
4,1
1,0
0.6
0,05
0.32
0.65
0.2
0.2
2
<0.1
<1.0
0.33
0.2
10,0
0.15
1.2
<5.0
0,75
<1.0
0.31
0,14
0,05
0.05
0.05
0.52
l.S
0.23
0.274
0.11
<0.06
0.03
1
0.03
Zn
Q.15
0.26
18.4
0,12
0.1
0.4
0.6
39,700
34,000
15,400
1,100
5,800
9,100
18,900
47,300
94, 600*
123,000
28,000
401,000
55,300
28,000*
78,700
68,000
39,700
47,300
11,000
3,800
28,400
3,100
42,600
44, 700
68,000
. 39., 400
34,TDOO
68,000
250,000
12,000
473,000*
55,300
2, $00*
170,000
30,000
91,000
8,700
62,500
32,500
42,600*
11,200
8,100
21,600
32,500
3,800
11,400
295,000
11,500
129,000
36,000
8,700
17,000
620*
(a) &ii fisteriek after the total flow means en assumed 8*hour work
liters per day was based dtt 24*"hour work 4 ay,
values could be lower by B factor of 3 If
139
-------
100
en
_c
_o
a.
c
tfl
^
a
CL
E
LU
O)
.a
e
0 10 20 30 40 50 60 TO 80 90 100
Cumulative Percent
FIGURE 18. EMPLOYEES PER SHIFT IN PLATING VERSUS
CUMULATIVE PERCENTAGE OF 53 PLANTS
140
-------
0»
i_
0>
cx
E
o
1,000,000
500,000
200,000
100,000
•£ 50,000
0)
O
T3
r: 20,000
o
•*—
o
10,000
5000
ZOOO
1000
0 10 20 30 40 50 60 70 80 90 100
Cumulative Percent
FIGURE 19. TOTAL INSTALLED CURRENT FOR PLATING
VERSUS CUMULATIVE PERCENTAGE OF
53 PLANTS
141
-------
500,000
200,000
100,000
50,000
20,000
Q.
£
o
£• 10,000
'
o
CL
D
O
£
c
5000
f 2000
1000
500
200
100
1 1 III!
I I fill
* *
5 10 20 50
Number of Employees per Shift
100
FIGURE 20. INSTALLED RECTIFIER CAPACITY IN AMPERES FOR
ELECTROPLATING VERSUS NUMBER OF EMPLOYEES
PER SHIFT IN ELECTROPLATING FOR 53 PLANT
SAMPLE (RATIO OF AMPERES USED TO AMPERES IN-
STALLED IS TYPICALLY 65 PERCENT)
142
-------
100
0 10 20 30 40 50 60 70 80 90 100
Cumulative Percent
FIGURE 21 .
EFFLUENT DISCHARGE RATE VERSUS
CUMULATIVE PERCENTAGE OF 53 PLANTS
143
-------
•that 50 percent of the 53 plants evaluated have an effluent of
less than 3^,000 1/hr. Most plants analyze for total metal and
oxidizable cyanide (rather than total cyanide). These
concentration values reported by the companies are typical
average values (monthly period or longer) . Figure 22 shows the
range of concentration of metals and cyanide (oxidizable)
typically achieved by those plants which report that pollution
parameter. The results are representative of chemical treatment.
Figure 22 shows that 50 percent of the plants have values less
than the following:
Cu 0.2 mg/1
Ni 0.5 nig/1
Cr*+ 0.055 mg/1
CrT 0.3 mg/1
Zn 0.3 mg/1
CN 0.04 mg/1.
From the limited data on total suspended solids in Table 28 about
half of the plants are achieving less than 15 mg/1.
Table 29 provides a comparison of the waste treatment results for
all 53 plants on the basis of total installed amperage. The
total plant effluent (1/hr) in Table 28 was divided by the total
installed current capacity (amperes) in Table 27 to obtain the
plant water "use (kg/AH which is numerically equivalent to 1/AH)
shown in Table 29. The water use multiplied by the
concentrations (mg/1) of each constituent in the treated effluent
shown in Table 28 gave "the waste discharged (mg/AH) shown in
Table 29. Table 29 provides an approximate intercomparison of
the waste treatment results for various plants for several
pollutant parameters over a wide range of plant sizes. The data
have been normalized by the use of total current. However, in
order to draw valid conclusions for direct comparison of two
plants in Table 29 additional information is needed on any
unusual differences in thickness of deposit (e.g., the two
extreme cases of thick chromium plating are noted) or the
fraction of -the rated current that is normally used (Table 27) .
Figure 23 shows that 50 percent of the 53 plants achieving a
water use of less than 1.35 I/AH (or kg/AH) based on total
installed current. The water used would be about 2.0 I/AH based
on the assumption of 67 percent of the rated capacity normally
used as indicated previously. Since the latter water use (I/AH)
is independent of the concentration values (mg/1) achieved in
chemical treatment, it is possible to multiply the median water
use and median concentrations to estimate the waste discharge
(mg/AH) which should be achievable for most plants:
Cu 0.4 mg/AH
Ni 1.0 mg/AH
Cr*+ 0.11 mg/AH
CrT 0.6 mg/AH
Zn" 0.6 mg/AH
CN(Oxid) 0.08 mg/AH.
144
-------
£
Q-
O.
UJ
-a
OS
a
05
0.05
0.02
0,01
0,005
0.002 —
0.001
0 10 20 30 40 50 60 70 80 90 100
Cumulative Percent
FIGURE 22, COMPOSITE OF POLLUTANT PARAMETERS IN TREATED
EFFLUENT VERSUS CUMULATIVE PERCENTAGE OF
PLANTS 145
-------
TABLE
COMPARISON OF TREAIED EFFLUENT BAXA BASED ON TOlAl AMPERAGE
Company
Code No.
1-16
3-1
3-3
3-4
6-3
6-12
6-29
8-4
8-5
11-8
11-13
11-22
12-3
12-5
12-8
12-8
12-9
12-12
13-2
15-1
19-2
19-3 <»>>
20-1
20-6
20-7
20-10
20-13
20-15
20-1?
21-3
23-3
25-1
28-9
28-11
30-1
30-5
30-7
30-8
33-1
33-2
33-3F
33-30
33-6
33-8 C«)
33-?
33-11
33-15
33-20
33-21
36-1
36-2
40-4
43-1
Classification
c/s/ccc-cc
C/S/--BEE-
C/S/-IEI-B
C/S/EB—BB
C/S/BII— B
C/M/ENCEEN
J/S/CCICIC
C/M/CCC-CC
C/l/CCC-CC
J/S/CCDECC
j/s/ccc-ce
C/M/000-BC
J/M/NEENNC
J/M/CCCCAC
J/S/TOE-BB
C/M/CCCCeC
c/s/m-ic
C/M/— EE-
C/M/COI-CC
C/M/— EE-
J/S/LCLLK
J/S/--I— C
c/s/c-cccc
C/S/CCB-BC
C/S/CCBCBC
C/M/-II--C
C/S/ICIIIC
C/M/-BB— B
C/S/CCCCCC
C/S/BBSBBB
J/M/.CCC-CC
C/M/CCCCCC
J/L/-B--BB
C/H/CGCCCC
J/M/ICLU.C
C/S/IIIIIC
C/S/III-IG
C/M/--NBBB
J/S/CCCCCC
C/S/BNN-SB
C/M/--IEEC
C/M/— IEEC
J/M/-CCC— C
C/S/--B— B
J/M/NBB-HG
C/M/C-CCCC
C/S/CCB-BC
C/M/CCCCCC
C/M/— CCCC
C/S/BBBBBB
C/M/INI-IB
C/S/DDD--C
C/S/RCRBBB
Water
Use.
ks/AHW
2,4
3,4
0,38
0,09
1.2
0.27
3.1
15.0
12.0*
1.3
1.5
5.5
1.5
2.0*
0.30
1.1
1.2
0.35
0.77
0.64
1.2
0.0?
12.0
0.77
2.1
0,55
3.1
7,7
2,0
5,9
6.4*
0,73
0,14*
1.3
1.5
9.1
0,44
4.2
0.65
34*
1.6
l.l
0.86
132
0.40
0,77
0.64
1,9
2.5
2.3
2,4
0.64
0.08
Waste Discharge, tnfi per AH
TSS
4.2
26
156
53
42
20
14
323
7,3
3.8
13
265
Cu
1.1
0.007
0.007
0.098
0.14
1,5
0.026
0.15
1.7
0.75
4.8
0.30
0.77
1.2
2.3
0.01
2.2
O.Q74
0,21
0.31
0.82
1.2
11.0
0.051
1.4
0.53
0.30
1.8
1.5
0.13
50
0.086
0.052
2.4
0.13
0,40
0,30
0,023
0.38
1.3
0.023
Nt
2.4
0.0003
0.043
0,74
5.3
1.9
0.90
0.21
0.05
2.3
4.4
0.30
0.22
1.2
•-
1.9
0.01
0.30
1.5
1.1
0.93
7.7
0.96
1.5
0.58
0.65
11
1,8
0.20
34
0,043
0.64
0.27
0.75
0,023
18
3.2
0.028
Cr+6
0.22
0.022
0.012
0.014
0.93
0.75
0.013
0.015
0.55
1.5
0.015
0.036
0.028
0.36
0.12
0,021
0.10
0,20
0.015
0.41
0.039
0.51
0,43
0.15
0,46
0.026
0.37
0.10
0.072
CrT
3,6
0.17
0,061
0.17
0.74
4.2
12.0
0.026
2.6
2.3
8.2
0.30
0.66
0,06
0.38
0.046
0.77
0,42
1.1
0.31
7.7
0.66
1.2
64.0
0.11
1.6
7.5
6.8
4.2
0.20
4.8
0.08
0.06
6,6
0.21
1.4
0.15
0.52
0,28
0.14
0.072
0.64
• 0.024
Zn
0.51
0.32
5.0
0.16
0.55
0.80
0.66
1.2
0.22
3,2
0.008
15.6
0.53
0.62
0.16
0.18
13.0
0.64
0.50
12
4.1
21
0,52
0.08
0,06
0,39
0.06
0.95
2,1
0.32
0.31
CN
0.22
0,12
0.30
0.22
0.15
0.12
0.013
0.015
9.8
19.8
0.06
0.11
0.03
0.35
0.77
1.9
1.2
0.72
0.008
0.021
0.31
0.003
0.059
1.3
0.022
0.0014
0,065
0.53
0.46
0.17
O.OS5
19
0,21
0.14
0.0077
0.016
0.015
0.13
0.023
0.048
0.0008
.(a) An asterisk after the water use means that calculations were baaed on an assumed 8-hour work day.
(b) Hard chromium only! multiply numbers by 50. No chromium was expected in effluent.
(c) Hard chromium only; multiply numbers by 50. Large water addition prior to treatment.
146
-------
E
QL
Q,
UJ
CD
: 0.2 -
0.001
0,05 —
0.02
0.01
0.005
0.002 -
0 10 20 30 40 50 60 70 80 90 100
Cumulative Percent
FIGURE 22. COMPOSITE OF POLLUTANT PARAMETERS IN TREATED
EFFLUENT VERSUS CUMULATIVE PERCENTAGE OF
PLANTS
145
-------
3XBLE
COMPARISON OF TTHEA1ED EFFLUENT Mtt BASED ON TOTAl AMPEBAGE
Company
Code No.
1-16
3-1
3-3
3-4
6-3
6-12
6-29
8-4
8-5
11-8
11-13
11-22
12-3
12-5
12-6
12-8
12-9
12-12
13-2
15-1
19-2
19-30")
20-1
20-6
20-7
20-10
20-13
20-15
20-17
21-3
23-3
25-1
28-9
28-11
30-1
30-5
30-7
30-8
33-1
33-2
33-3F
33-3U
33-6
33-8fc)
33-9
33-11
33-15
33-20
33-21
36-1
36-2
40-4
43-1
Classification
c/s/ccc-cc
C/S/— BEE-
C/S/-IEI-B
C/S/EB--BB
C/S/B1I— B
C/M/ENCEEN
J/S/CCICIC
C/M/CCC-CC
C/l/CCC-CC
J/S/CCDECC
J/S/CCC-CC
C/K/000-BC
J/M/HEEHNG
J/M/GCCCAC
J/S/BDE-BB
C/M/CCCCCC
C/S/IRI-IC
C/M/— EE-
C/H/COI-CC
C/M/— EE-
J/S/LCUiC
J/S/--I--C
c/s/c-cccc
C/S/CCB-BC
C/S/CCBCBC
C/M/-II— C
C/S/ICIIIC
C/M/-BB--B
C/S/CCCCCC
C/S/BBBBBB
J/M/CCC-CC
C/M/CCCCCC
J/L/-B--BB
C/M/CCCCCC
J/M/ICLUC
c/s/miic
C/S/III-IC
C/M/--NBBB
J/S/CCCCCC
C/S/BSM-SB
CM/— IEEC
C/M/— IEEC
J/H/CCC— C
C/S/— B— B
J/M/NDO-SC
C/M/C-CCCC
C/S/CCB-BC
C/M/CCCCCC
C/M/--CCCC
C/S/BBBBBB
C/M/INI-IB
C/S/DDJ)— C
C/S/ECRBBB
Hater
Use
fcg/AHW
2,4
3,4
0.38
0.09
1.2
0.27
3.1
15. Q
12.0*
1.3
1.5
5.5
1.5
2.0*
0.30
1.1
1.2
0,35
0.77
0.64
1.2
0.07
12.0
0.77
2.1
0.55
3.1
7.7
2.0
5.9
6.4*
0.73
0.14*
1.3
1.5
9.1
0.44
4.2
0.65
34*
1,6
1.1
0.86
132
0,40
0.77
0.64
1.9
2.5
2.3
2.4
0.64
0.08
Haste Discharge, me tier AH
TSS Cu
1.1
0.007
0.007
4.2 0.098
0.14
1.5
0.026
0.15
1.7
0.75
4.8
0.30
26 0.77
1.2
2.3
0.01
156 2.2
0.074
53 0.21
0.31
42 0.82
1.2
11.0
0.051
1,4
20 0.53
0.30
1.8
1.5
14 0.13
323 50
7.3 0.086
3.8 0.052
2.4
13 0,13
0,40
265 0.30
0.023
0.38
1.3
0.023
Ni
2.4
0.0003
0.043
0.74
5.3
1.9
0,90
0.21
0.05
2.3
4.4
0,30
0.22
1.2
**
1.9
0.01
0,30
1.5
l.i
0.93
7.7
0.96
1,5
0,58
0.65
11
1.8
0.20
34
0.043
0.64
0.27
0.75
0.023
18
3.2
0,028
Cr«
0,22
0.022
0.012
0.014
0.93
0.75
0.013
0.015
0.55
1.5
0.015
0.036
0,028
0,36
0.12
0.021
0.10
0.20
0.015
0,41
0.039
0.51
0.43
0.15
0.45
0.026
0.37
0.10
0,072
CrT
3.6
0.17
0.061
0.17
0.74
4.2
12.0
0.026
2.6
2,3
8.2
0.30
0.66
0.06
0.38
0.046
0.77
0.42
1,1
0,31
7.7
0.66
1.2
64.0
0.11
1.6
7,5
6.8
4.2
0.20
4.8
0.08
0.06
s.s
0,21
1.4
0.15
0.52
0.28
0.14
0.072
0.64
0.024
Zn
0.51
0,32
5.0
Q,i£
0.55
0.80
0,66
1.2
0.22
3.2
0,008
15.6
0.53
0.62
0.16
0.18
13.0
0.64
0.50
12
4.1
21
0.52
0.08
0,06
0.39
0.06
0.95
2.1
0.32
0.31
CM
0.22
0.12
0.30
0.22
0.15
0.12
0.013
0.015
9.8
19.8
0.06
0.11
0.03
0.35
0.77
1.9
1.2
0.72
0.008
0.021
0.31
0.003
0.059
1.3
0.022
0,0014
0.065
0.53
0.46
0.17
0.025
19
0,21
0.14
0.0077
0.016
0,015
0,13
0.023
0,048
0.0008
(a) An asterisk after the »ater use means that calculations were based on an assumed 8-hour work day.
(b) Hard chroratura only; multiply number* by 50. Ko chromium »as expected in effluent.
(e) Hard chromium only; multiply numbers by 50. large water addition prior to treatment.
146
-------
100
0 10 20 30 40 50 60 70 80 90 100
Cumulative Percent
FIGURE 23. WATER USE BASED ON TOTAL INSTALLED CURRENT
VERSUS CUMULATIVE PERCENTAGE OF 53 PLANTS
147
-------
A comparison of the above values with those in Table 29 shows
that many plants attain lower values for a single pollution
parameter. However, for all pollution parameters (all metals and
cyanide) the above values are attained by only 11 plants in Table
29 (3-1, 3-3, 3-4, 11-8, 12-6, 19-3, 25-1, 33-1, 33-15, 36-1, and
43-1).
Four of these plants were chosen for further study. Figure 24
shows that those plants (15) that are using some combination of
in-process control for chemical recovery (evaporation, ion
exchange, reverse osmosis) in one or more plating operations have
lower water use than those plants (38) that do not use such in-
process controls. The apparent two-to-three-fold reduction is
water use in probably indicative of the general use of multitank
countercurrent rinsing and other water conservation practices in
these plants.
Figures 25 through 31 show the data of Table 29 on performance
being obtained by various plants separately for each parameter:
copper, nickel, hexavalent chromium, total chromium (Cr+3 +•
Cr+6), zinc, cyanide (amenable to oxidation by chlorine) and
suspended solids. For a general estimate, a value of 40 to 80
AH/sq m can be used to convert waste discharged from mg/AH to
mg/sq m and water use from kg/AH (or 1/&H) to kg/sq m (or 1/sq
m) . A value of 60 AH/sq m corresponds to the following
thicknesses of the various plated metals:
Metal Cur Ef f... % __njils
Cu 100 0.31
Ni 100 0.29
Cr 13 0.014
Zn 60 0.24
The various waste management technologies were identified by
symbols in Figures 25 through 31. The appropriate symbol is used
for each parameter to show whether a reduction in quantity of
waste discharged was achieved as the result of using the
particular technology.
Continuous (flow through) chemical treatment is the baseline
technology for reference with inplant segregation of chromium and
cyanide streams for separate treatment prior to recombination
with the remaining waste streams (acid/ alkali and others) for
final separation of precipitated metals. The use of this
technology provides the best overall results for all parameters
because its use insures complete treatment of the acid/alkali
stream to remove precipitated metal.
Complete batch chemical treatment of all segregated streams is an
alternative to continuous chemical treatment that can provide
equivalent pollution reduction. Batch chemical treatment of only
the hexavalent chromium and cyanide streams (Figure 16 and 19)
combined with continuous chemical treatment for metal removal
148
-------
100
50
20
10
Q.
E
o
3
0.5
0.2
0.!
0.05
0.02
0.01
1 T
No in-process
recovery system
**
Some in-process
recovery system
0 10 20 30 40 50 60 70 80 90 100
Cumulative Percent
FIGURE 24. COMPARISON OF THE WATER USE FOR PLANTS THAT
USE IN-PROCESS-CHEMICAL RECOVERY SYSTEMS ON
ONE OR MORE PLATING OPERATIONS WITH THE WATER
USE OF PLANTS THAT DO NOT USE IN-PROCESS RECOVERY
149
-------
Cn
O
1000
(00
10
A
D
O
O
A
~~> ^n '
Continuous chemicol treatment
Integrated chemical
Botch chemical treatment
Ion exchange
Electrolytic
No treatment
Evaporation
Reclaim rinse
10
100
Water Use, kg/amp hr
FIGURE 25 . COPPER IN TREATED EFFLUENT FROM ELECTROPLATING
-------
1000
100
0.10
0.01
0,001
0.0001
Continuous chemical treatment
Integrated chemical
Batch chemical treatment
Ion exchange
Electrolytic
No treatment
Evaporation
Reclaim rinse
Adsorption
o.oi
O.IO
I.O
10
100
Water Use, kg/amp hr
FIGURE 26. NICKEL IN TREATED EFFLUENT FROM ELECTROPLATING
-------
U1
to
1000
100
CL
O
10 —
1.0
aio
0.01
aooi
0.0001
0.01
D
O
O
I i i I i
Continuous chemical treatment
Integrated chemical
Batch chemical treatment
Ion exchange
Electrolytic
No treatment
Evaporation
Reclaim rinse
Adsorption
i I i
i I r
0.10
1.0
Water Use, kg/amp hr
10
100
FIGURE
27
HEXAVALENT CHROMIUM IN TREATED EFFLUENT FROM ELECTROPLATING
-------
1000
Ul
U)
Q 0.10 —
O.O1 —
Q001
0.0001
Continuous chemical treatment
Q Integrated chemical
O Batch chemical treatment
Ion exchange
Electrolytic
No 'treatment
Evaporation
Reclaim rinse
30-1A "2-5
X Adsorption
0.01
10
100
Water Use, kg/amp hr
FIGURE 28 . TOTAL CHROMIUM IN TREATED EFFLUENT FROM ELECTROPLATING
-------
1000
100
10
ex
I
0.10
0,01
QOOt
QOOOI
QOi
o
o
o
A
Continuous chemical treatment
Integrated chemical
Batch chemical treatment
Ion exchange
Electrolytic
No treatment
Evaporation
Reclaim rinse
Adsorption
QIO
to
100
Water Use, kg /amp hr
FIGUR^ 29 . ZINC IN TREATED EFFLUENT FROM ELECTROPLATING
-------
H
tn
ui
ET
o
1000
100
10
1.0
0.10
0.01
0.001
I I I
i I T
a
Continuous chemical treatment
Integrated chemical
O Batch chemical treatment
O Ion exchange
Elect roiytic
No treatment
Evaporation
Reclaim rinse
.01
O.IO
I.O
Water Use, kg/amp hr
IO
100
FIGURE 30. CYANIDE IN TREATED EFFLUENT FROM ELECTROPLATING
-------
en
en
1000
100
10
Q.
o
0,10
0.01
0.001
0.0001
001
O.iO
1.0
Water Use, kg/amp hr
100
FIGURE 31 SUSPENDED SOLIDS IN TREATED EFFLUENT FROM ELECTROPLATING
-------
does not provide significantly greater pollution reduction
(Figures 14, 15, 17, and 18).
All other technologies currently in use for in-process treatment
after one or more plating processes such as integrated chemical
treatment, are combined with end-of-process continuous or batch
treatment of at -least the acid/alkali stream for removal of
metals. Where there is no treatment prior to discharge beyond pH
adjustment, the effluent may contain a high level of pollutants.
There was no evidence from plant data that any in-process
treatment achieved greater pollution reduction than that which
can be achieved by end-of-process chemical treatment.
In-process controls used after plating operations for recovery of
chemicals such as evaporation, ion exchange, reclaim rinses, and
reverse osmosis and/or reduction of water use are combined with
end-of-process chemical treatment, without chemical treatment,
the effluent may contain a high level of pollutants,' Thus, there
is presently no evidence that greater pollution reduction than by
chemical treatment can be achieved by use of these technologies.
Closing up one or all plating operations by evaporative
technology does not presently succeed in eliminating the
pollution parameter from the final effluent. In general, the
present use of the above in-process controls does not lead to a
significant reduction in pollution for the total electroplating
facility which includes rinse water after pretreatment and
posttreatment operations.
The above conclusions based on the degree of pollution reduction
achieved by existing sources indicates that end-of-process
chemical treatment in combination with in-process controls for
water conservation is the Best Practicable Control Technology
Currently Available for existing sources in the electroplating
industry.
In using the term chemical treatment no distinction is made
between continuous chemical treatment, batch chemical treatment,
integrated chemical treatment or ottyer in-process treatments or
combinations provided that the efficient limitations are achieved.
No distinction is made in the specific chemicals used, specific
chemical reactions, or specific processes employed for
destruction of cyanide, reduction of hexavalent chromium, or
removal of metals provided the effluent limitations are achieved.
In using the term in-process controls, no distinction is made
between the various methods of Recovery of chemicals or water
conservation. Effluent limitations ican be achieved by either
reduction in water use or reduction
in concentration of pollutant
after final treatment or both. It is recognized that the results
attainable with any waste- management technology are dependent on
correct operation of the process, the maintenance of control
instrumentation, and the quality and capability of operating and
supervisory personnel.
Detailed Analysis of Plant Data
15?
-------
From the above analysis of data from 53 plants, 5 plants were
selected for additional on-site detailed analysis of plating
operations for correlation with in-process controls for water
conservation and waste treatment results including sampling to
verify effluent data reported. One of the plants selected (19-3)
had only hard chromium plating operations which is a special
situation because of the thick deposit. The other four plants
(11-8, 12-8, 33-1, and 36-1) were selected as representative of
the average of the best plants involved in rack and barrel
electroplating of copper, nickel, chromium and zinc,
The data obtained from each of the four second-round plant visits
were analyzed with respect to the various pertinent process lines
of rack and barrel plating of copper, nickel, chromium, and/or
zinc. Hon-pertinent process lines (e.g., anodizing, bright
dipping, cadmium plating, or other than rack and barrel plating)
were not included as well as certain pertinent process lines not
in use or for which insufficient data were available. The
composite of the pertinent lines was also analyzed. The purpose
of the analysis was to study water use.
The various factors based on the composite of process lines are
shown in Table 30. The monthly average concentration of each
pollutant parameter reported by the plant multiplied by the
specific water use (I/AH) or effluent factor (1/sq m) yields the
waste discharge in mg/AH or mg/sq m respectively as shown in
Table 31. The values can be compared to the recommended 1977
effluent limitations for existing sources for copper, nickel,
chromium (total), zinc, and total cyanide (80 mg/sq m) and for
heKavalent chromium and oxidizable cyanide (8 mg/sq m) and for
suspended solids (2400 mg/sq m) .
For comparison, the corresponding data using the results of
sampling and analysis on the day of the plant visit and the
appropriate water use factors from Table 30 are shown in Table
32.
For plants required to analyze daily composite samples for
monthly reporting to authorities, the monthly averages over a
prior period of 6 to 12 months were used to determine typical
average concentrations of pollutants. In general, the latter
value is more representative of waste treatment results than
samples obtained over a short period during a plant visit.
However, for Plant 33-1, the average results for 1972 were
considerably higher than those obtained after about June 1972, as
shown in Table 33. A significant reduction in concentration of
metals occurred coincident with reduction of suspended solids
concentration as a result of improved clarification. The
concentrations currently achieved in 1973 are lower than the
average values used previously in Table 31 to determine mg/AH and
mg/sq m for each pollutant parameter.
Daily variations in concentrations of metals and cyanide in
treated effluent compared to the monthly average are to be
expected. Figure 32 shows the typical variation in analysis of
158
-------
TABLE 30. fUMMARY OF WATER USE PARAMETERS FOR FOUR
* PLANTS BASED ON COPPER, NICKEL CHROMIUM
OR ZINC PLATING AND EXCLUDING NON-
PERTINENT METAL FINISHING PROCESSES
Company
No.
Specific
Water Use,
I/AH
Effluent Coulombic
Factor, Equivalent Factor,
1/sq m AH/sq m
11-8
12-8
33-1
36-1
average
2.44
1.77
1.34
1.08
1.66
159
-------
TABLE 31. SUMMARY OF TREATED EFFLUENT FROM COPPER, NICKEL,
CHROMIUM OR ZINC EXCLUDING NON-PERTINENT PLANT
METAL FINISHING OPERATIONS
Pollutant
Parameter
Cu
mg/1
mg/AH
mg/sq m
N1
mg/1
mg/AH
mg/sq m
Cr(Hex)
mg/1
mg/AH
mg/sq m
Cr(Tot)
mg/1
mg/AH
mg/sq m
Zn
mg/1
mg/AH
mg/sq m
CN(Ox)
mg/1
mg/AH
mg/sq m
Plant
11-8
.03
.07
5.1
.16
.39
27.2
.01
,02
1.7
.02
.05
3.4
.12
.29
20.4
.01
.02
1.7
Plant
12-8
.70
1.24
86. 8
,20
.35
19.1
--
--
--
.60
1 .06
57.3
.60
1.06
57.3
.01
.18
9.6
Plant
33-1
.20
.27
15.5
.30
.40
23.2
.06
.08
4.6
.31
.42
24.0
.80
1.07
61.9
.13
.17
10.0
Plant
36-1
.03
.03
3.4
.02
.02
2.3
.01
.01
1.7
.06
.06
6.8
.14
.15
16.0
.01
.01
1.1
Average
.24
.40
22.7
.17
.29
18.0
.03
.04
2.7
.25
.40
22.9
.41
0.64
38.9
.06
.10
5.6
160
-------
TABLE 32 t SUMMARY OF TREATED EFFLUENT
SAMPLING AND ANALYSIS DURING SECOND
ROUND VISIT FOR COMPARISON WITH TABLE 2
Pollutant
Parameter
Cu
mg/1
mg/AH
mg/sq ra
Ni
mg/1
mg/AH
mg/sq ra
Cr (Hex)
mg/1
mg/AH
mg/sq m
Cr(Tot)
mg/1
mg/AH
rag/sq m
Zn
mg/1
mg/AH
mg/sq m
CN (Tot)
mg/1
mg/AH
mg/sq m
SS
mg/1
mg/AH
mg/sq m
Plant
11-8
.07
.17
12
.54
1.32
92
.15
.37
25
.33
.80
56
.49
1.20
83
.78
4.64
133
—
- —
—
Plant
12-8
.33
.58
31
.17
.30
16
.65
1.15
62
1.33
2.35
127
.42
.74
40
.22
.39
21
24
42
2292
Plant
33-1
.46
.62
36
.22
.29
17
.05
,07
4
.20
.27
15
,90
1.21
70
.21
.28
16
22
29
1701
Plant
36-1
3.16
3.41
360
.44
.47
50
.05
.05
6
.28
.30
32
.66
.71
75
.13
.14
15
20
22
2280
Average
.29
.46
26
.34
.60
44
.22
.41
24
.54
.93
57
.62
.96
67
.33
1.36
46
22
31
2091
161
-------
1
O
+
u.
o
u
Q
Q.
C O
">o
So
170
U. we
0 GO
01 A
Orn
OAfi
.uu
01 A
. 1 V
0 30
0?n
Oin
.IV
0 OO
Onx
On i
.V 1
OAA
noo
'
*
*
«
9
<
,
•
«
*
*
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5 10 15 20 25 5 iO 15 20 25 5 10 15 20 25 5 10 15 2025
January February March April
FIGURE 32, TYPICAL VARIATION IN CONCENTRATION OF POLLUTANT
PARAMETERS FROM ANALYSIS OF DAILY COMPOSITE OVER
A 4-MONTH PERIOD REPORTED BY PLANT 11-8
162
-------
daily composites over a 4-month period for Plant 11-8. Because
of the low concentrations being measured, daily concentrations
are at times twice the monthly average concentration. One factor
is analytical accuracy. For example, in the measurement of
copper (1 mg/1), chromium (0.05 mg/1) and zinc (0.5 mg/1) by
atomic absorbtion methods the relative standard deviations are
11, 26, and 8 percent respectively (4). Another factor is that
daily composite samples are usually analyzed the day follpwing
collection. Thus, there is a 24-hour time lag in detection of
slight changes in waste treatment performance before corrective
action is taken. In view of the above factors and determination
of plated area, effluent limitations should be based on
cumulative 30-day averages with an allowance for daily maximums
exceeding the 30-day average by a factor of 2.
petermipati.gn of if fluent Limit atioos
The quantitative effluent limitations based on Best Practicable
Control Technology Currently Available for existing sources
discharging to navigable waters to be achieved by 1977 were
listed in Table 1. The quantitative values were based on
determination of what can be achieved by the average of the best
plants in the electroplating category. The values are based on
technical consideration of what concentrations of pollutants in
the treated effluent can be achieved by chemical treatment and
technical consideration of what reduction in water use for
rinsing can be achieved by normal practice by existing sources in
the electroplating industry. The basis for the 30-day effluent
limitations will be reviewed first considering the heavy metal
pollutants.
For copper, nickel, total chromium, and zinc it is possible to
achieve 80 mg/sq m as was shown for the average of four plants
analyzed in detail. In addition, the average of the median
values for copper, nickel, chromium, and zinc for 53 plants is
about 0.3 mg/1. Thus, the effluent limitations can be met with
an effluent factor as high as 267 1/sq m. The median water use
of 53 plants was shown to be about 1,3 1/AH based on rated
current or about 2 1/AH based on typical current used. Thus, a
coulombic factor of 60 AH/sq m based on typical deposit
thicknesses indicates an effluent factor of 120 1/sq m.
Water use less than 120 1/sq m can be achieved using good rinsing
practice. For example, an automatic copper, nickel, chromium
rack plating operation with 22 1/sq m and two different zinc
platers (with chromate conversion) achieved 45 1/sq m. The above
values were attainable by use of good in-process control without
the use of any advanced recovery techniques.
Allowing for the fact that all existing sources may not be able
to use optimum water conservation because of space limitation for
additional rinse tanks, a value of 160 1/sq m appeared to be
broadly applicable. Thus, the combination of an effluent volume
of 160 1/sq m and a concentration of 0,5 mg/1 for copper, nickel,
total chromium, and zinc, a concentration of 0.05 mg/1 of
163
-------
hexavalent chromium and oxidizable cyanide and a concentration of
15 mg/1 of total suspended solids appeared to be technically
achievable. Tentative effluent limitations, consisting of the
products of 160 1/sq m and the concentrations, may then be listed
as follows:
Cu 80 mg/sq m
Ni 80 mg/sq m
Cr (total) 80 mg/sq m
Zn 80 mg/sq m
Cr (hexavalent 8.0 mg/sq m
CN- (oxidizable) 8.0 mg/sq m
To test how many of the 53 plants would be in compliance with
these tentative effluent limitations, the values in Table 29 for
various constituents (except TSS) in mg/AH were multiplied by 60
AH/sq m to give products in units of mg/sq m that could be
directly compared with the above values. The result of this
analysis was that plants could meet the effluent limitations
without questions, plants could meet the guidelines for the
constituents reported, but did not report all of the constituents
that should have been present in their effluent. Plant 33-1 of
the four pertinent plants studied in detail (Table 31) met the
tentative effluent limitations compliances for various values of
effluent limitations were studied and results are summarized in
Table 33.
The effluent limitations of 80 mg/sq m for copper, nickel, total
chromium and zinc and of 8.0 mg/sq m for hexavalent chromium and
oxidizable cyanide are achieved by at least 10 plants according
to the reported data. The verification data obtained indicate
that at least two plants (33-1 and 11-8) can achieve these
limitations. The limitations are achieved through water
conservation and treatment of waste water to yield low
concentrations of these components with effluent. The
achievement of these effluent limitations by these plants
constitutes the basis for preparing them for standards to be
achieved by 1977.
The effluent limitation for total cyanide of 80 mg/sq m was based
on a concentration of 0.5 mg/1 combined with an effluent factor
of 160 1/sq m. some plants may analyze for total cyanide and
report the value simply as cyanide meaning maximum oxidizable as
well as total cyanide. However, some plants report oxidizable
cyanide only. The average value determined by analysis of
samples from the four plants tudied in detail was less than 0.5
mg/1 total cyanide. Three of the four plants had 20 mg/m2 or
less.
The effluent limitation for total suspended solids of 2400 mg/sq
m was based on an effluent factor of 160 1/sq m combined with a
concentration of 15 mg/1 achieved by over half of the plants for
which data was available. The value for three plants during
visits was 22 to 24 mg/1 representative of a single day.
164
-------
TABLE 33. COMPLIANCE OF ELECTROPLATING FACILITIES
WITH EFFLUENT LIMITATIONS GUIDELINES
Effluent Limitation - 30 Day Average
Cu, Ni, CrT, Zn Cr+6, oxidlzable CN
mg/sq m/op mg/sq m/op
No. of plants
meeting guide-
lines on basis
of industry data
Additional plants
meeting guidelines
but "lacking some
data
Plants verified
meeting guide-
lines
40
4.0
t-l
CTi
cn
60
80
6.0
8.0
100
120
10.0
12.0
(3-1, 3-3, 11-8,
25-1, 36-1)
(above + 33-1)
10
(above + 6-3,
12-8, 12-9,
20-10)
13
(above + 20-7,
28-9, 30-7)
15
(above, + 20-7
28-11)
(3-4, 12-6,
33-15, 43-1)
4
(above)
(above + 20-6)
8
(above + 21-3,
33-30, 33-9)
8
(above)
(33-1)
1
(above)
1
(above)
1
(above)
1
(above)
-------
TABLE 34 , MONTHLY AVERAGE EFFLUENT CONCENTRATION
FOR PLANT 33-1 SHOWING IMPROVED RESULTS
OBTAINED OVER A 14-MONTH PERIOD
Chromium
Year Month
1972 Jan.
Feb.
Mar.
Apr.
May
June
July
Aug.
Sept.
Oct.
Nov.
Dec.
1973 Jan.
Feb.
Mar.
Apr.
Cd
0.31
0.28
0.26
0.54
0.15
0.03
0.07
0.03
0.03
0.01
0.01
0.18
0.05
0.05
0.05
0.09
Cr°^
0.08
0.15
0.12
0.05
0.05
0.04
0.04
0.04
0.05
0.03
0.05
0.03
0.01
0.02
0.01
0.02
Cr^+
1.07
1.45
0.08
0.70
0.30
0.16
0.16
0.26
0.15
0.07
0.05
0.05
0.06
0.10
0.02
0.03
1
0
1
1
1
1
0
0
0
0
0
0
0
0
0
0
Cu Fe
.6
.80 —
2
.30
.10
0 — —
.30 0.30
.60 0.20
.80 0.20
.20 0.10
.20 0.30
.15 0.20
.10 0.20
.03 0.08
.09 0.09
.07 0.20
Ni
—
—
—
—
—
—
0.30
0.60
0.60
0.80
0.70
0.20
0.20
0.10
0.10
0.06
Zn
5.6
16.0
24.0
8 '.50
2.40
0.2
0.20
0.20
0.20
0.10
0.20
0.20
0.10
0.09
0.03
0.20
CN
0.08
0.08
0,09
0.06
0.06
0.12
0.10
0.11
0.10
0.10
0.02
0.02
0.02
0.01
0.01
0.02
S.
18
32
52
27
12
8
10
10
10
15
11
12
11
8
11
11
S.
.9
.50
.0
.0
.0
.0
.0
.4
.1
.9
.0
.6
PH
7.5
7.6
7.2
8.3
8.4
8.9
8.4
8.1
8.9
8.8
8.5
7.9
7.6
7.8
7.9
7.7
(1) Averaged concentrations for each month are in mg/1 for daily composite
analysis of waste water,
166
-------
A 9-month average value of about 10 mg/1 achieved by one of the
plants was considered representative.
The above values used in determining effluent limitations a
summarized in Table 36 in terms of concentration of the polluta
parameter in mg/1 for selected effluent factors in 1/sq m, t
product of which corresponds to the effluent limitations of Tab
1 in mg/sq m. The concentrations of Schedule A and B in t
interim guidelines for the electroplating industry as shown f
comparison. In general, the concentration values of Schedule
are similar to those for an assumed effluent factor of 80 1/sq i
The latter values on which effluent limitations are bas<
represent what is technically achievable; the desired values :
Schedule A were derived with consideration of water quality ar
stream standards.
The effluent limitations for BPCTCA in Table 1 are based on tota
metal rather than dissolved metal for several reasons, bu
principally because insoluble metal hydroxides can redissolv
depending on the pH of the receiving body of water. The need t
limit insoluble metal in the effluent has been recognized for
long time (e.g., the limit of 1/mg/l for insoluble metal for Cu
Ni, Zn and 0.25 mg/1 for Cr in Schedule A). This is the reaso
that good clarification and separation of suspended solids prio
to stream discharge has been practiced for many years. Since th.
plant effluent is usually discharged at the same pH thai
clarification occurs, the soluble metal concentration will
usually be significantly less than the total metal concentration.
Analysis for total metal only reduces the expense of plant
monitoring of the effluent discharge.
Additional Factors ^Considered^iinLSelection
of_Best_Practicable Control Technology
Currently^Available
Total Cost of Application of Technology in Relation to
Effluent Reduction Benefits
Based upon information contained in Section VIII of the report,
the average cost of chemical treatment prior to discharge of
effluent to surface waters from medium sized and large plants, is
$10.70/100 sq m, (9.9/1,000 sq ft). This cost averages tt
percent of the plating cost and normally will be less than 5
percent of the plating cost for most plants. The application of
this technology can achieve an 85 to 99 percent reduction in
pollutants in the effluent discharged to surface waters.
Cost of chemical treatment in small plants are greater than
$10.70/100 sq m (9.91/1000 sq ft) as indicated in Table 22.
Cost for small plants increase as size decreases because there is
a minimum capital investment ($50,000) for a chemical waste
treatment facility.
167
-------
TABLE 35 COMPARISON EFFLUENT LIMITATIONS FOR BPCTCA (TABLE I )
IN TERMS OF CONCENTRATION FOR VARIOUS FACTORS WITH
THE PRIOR INTERIM GUIDELINE CONCENTRATIONS
Parameter
Cu
N1
Cr6+
CrT
Zn
CN.oxid.
CN, total
TSS
Effl
40
2
2
0.2
2
2
0.2
2
60
Concentration^3), wg/1
uent Faetor(b),
1/sq m
80
2
2
.1
.1
1
.1
1.
30
160
.5
.5
.05
.5
.5
.05
.5
15
Schedule A ((
1.2(0.2)
2.0(1.0}
0.25(0.1)
1.5(0.5)
0.03
0.5
10
/ ^ \
") Schedule B^;
1.5
3.0
0.1
0.5
2.0
0.1
1.0
50
(0.5)
(2.0)
(0.2)
(1.0)
(a) Total metal (soluble metal in parenthesis for Schedules A and B)
(b) The product of the assumed effluent factor and concentration
is the effluent limitation in mg/sq m.
(c) Schedules A and B interim guidelines for the electroplating
industry.
168
-------
Size and Age of Equipment and Facilities
The size of the electroplating facility in terms of surface area
plated or the ampere-hours used does not affect the raw waste
load concentration and the degree of pollution reduction
attainable by application of the waste-treatment technology* The
cost of applying the technology is not significantly different
when expressed as percentage of plating costs for a wide range of
plant sizes with the exception of the very small plants discussed
above.
Age of waste-treatment facilities is a factor that will affect
the capital cost outlay. This will be greatest for those plants
not presently treating waste prior to discharge to surface
waters. Modest investments will be required to update some
existing treatment facilities to meet the effluent limitations.
Recently constructed or updated facilities might not require any
further capital investment. Some small increase in operating
costs may be required to achieve the effluent limitations but the
total cost of application of the technology would not exceed that
based on the average of the best plants.
Some existing sources have a large investment in automatic
plating machines which are difficult or expensive to modify for
installation of additional rinse tanks after pretreatment and
posttreatment operations. For other existing sources where space
is at a premium it might be expensive and sometimes impractical
to redesign existing plating lines or redesign the entire plating
facility to accommodate additional rinse tanks for optimum water
conservation on all operations. For these reasons, extending in-
plant controls for water conservation to closed-loop operation
and/or multitank rinsing following alkaline cleaners and acid
dips was not considered practicable for all existing sources.
without such currently available in-process controls to reduce
rinse water usage, other advanced technology designed to close up
the plant with complete reuse of water to achieve no discharge of
pollutants cannot be considered for existing sources except in
special situations. It should be noted that limitations of space
for sufficient rinse tanks would not apply to design of a new
plating facility. Also, the limitations of space within existing
automatic machines as older eqiupment if retired over the future
years. Thus, age of equipment and facilities is a factor that
influences what is practical to accomplish over the years.
Because of the above factors. Best Practicable Control Technology
Currently Available for existing electroplating facilities in the
industry would not eliminate discharge of pollutants.
Processes Employed
The possible variations in electroplating processes within a
single existing facility were also considered. complete
segregation of single-metal waste streams was not considered
practical, baseid on spatial limitations and economics. Stream
integration dilutes one process wastewater with at least one
169
-------
other. Although the total volume in which a specific waste water
constituent is present can thereby be increased so that the total
amount dissolved is increased, the solubility is still so low
that the constituent is still removed to a very high degree by
precipitation and clarification.
In defining the Best Practicable Control Technology, no special
allowance was made for variations in product design or shape
factor. If the shape of the parts being plated requires the use
of in-process controls such as countercurrent rinsing,
evaporation, or other advanced recovery systems for achieving
reduced water use to counteract the effect of unusually high
dragout, any supplemental cost should be added to the cost of
plating. Any such incremental increase in the cost of plating
will direct attention to the design of parts that drain more
easily to reduce dragout. This rationale of shifting the added
cost, if any, of increased pollution control to the
electroplating process simplifies the application of effluent
limitations and places it on an equitable basis. However,
provision has been made for specific modification in effluent
limitations upon proof of need for exceeding the volume of water
flow reflected in these recommended guidelines due to excessive
dragout that is not amenable to available control technology
discussed in Section VII. It is not the intent that the
recommended guidelines be inflexible with regard to the shape
factor such that exorbitant treatment costs would be required.
Nor was it intended to deprive the public of electroplated
products it needs. Permission to exceed effluent limitations
should be granted in cases where high dragout caused by unusual
shape complexity is not amenable to handling with current
available technology with equipment available to a specific plant
pending new product design to minimize the shape factor and/or
equipment modification.
Engineering Aspects of the Application of Various Types of
Control Technology
Advanced in-process controls for recovery of plating chemicals
are rapidly gaining acceptance and often show a net cost savings
compared to chemical treatment. However, the applicability of
these in-process controls is dependent on first achieving
reduction in water use by multitank countercurrent rinsing.
Process Changes
Process changes are not currently available to the electroplating
industry that would lead to greater pollution reduction than can
be achieved by the recommended effluent limitations. Some
possible process changes such as use of noncyanide plating baths
may eliminate one pollution parameter, but do not eliminate all.
They may be useful especially with regard to the smaller
facilites (those plating less than 33 sq m/hr or having an
installed capacity of less than 2000 amperes) for reducing the
cost of meeting the effluent limitations recommended in this
document.
170
-------
Nonwater Quality Enviromervtal Impact
As discussed in Section VIII of this report, the principal
nonwater quality aspect: of electroplating waste treatment is in
the area of solid waste disposal. Disposal of sludges resulting
from metal removal by chemical treatment is a current problem in
many states that have a high concentration of electroplating
facilities. The problem would be partially alleviated by
disposal of drier sludge. Such added costs for removal of water
from sludge would be imposed by the requirements for solid waste
disposal and does not directly result from the requirement for
water-pollution reduction.
The use of advanced technology to recover metal plating chemicals
from rinse water rather than chemical treatment which adds to the
sludge is being applied in areas where the sludge-disposal
problem is greatest. Further impetus in the direction of
recovery rather than disposal is expected to be provided by
authorities responsible for solid waste disposal. This will have
an overall beneficial effect on water pollution because of the
concurrent requirements for water conservation for economic
application of recovery techniques.
It is estimated that many of the existing electroplating sources
discharging to navigable waters are already using chemical
treatment methods with a high percentage removal of metals. This
is particularly true in geographic areas where water pollution
reduction has been emphasized and the sludge-disposal problem is
most evident. Achieving the effluent limitations by application
of chemical treatment technology will have little impact in total
quantity where solid waste disposal is a problem.
There will be no direct effect on air quality as a result of the
application of recommended technology for water-pollution
reduction. Indirect effects related to increased energy use will
be minor. Energy requirements (mainly electrical) for chemical
treatment are estimated to be 3.2 percent of the power needed for
electroplating.
Gu2.de|jtpes^|Qr_the Application
of Effluent L|mj.tatigng
Selection of Production Unit
Effluent limitations are intended to specify the maximum quantity
of pollutants which may be contained in the discharged treated
effluent from a point source. This quantity must be related to a
unit of production so that the effluent limitations can be
applied broadly to various plants in the same category regardless
of their production capacity. For example, an effluent
limitation for a particular wastewater constituent in mg/unit
times the production rate in units/hr equals the maximum amount
of that constituent that can be discharged in mg/hr. Thus, for
any production unit;
171
-------
mq X Unit = mg X 1 ,
unit ~te" 1 hr" Eguatxon 1
The right-hand side of the above equation represents the normal
method of monitoring based on analysis of concentration of
individual pollutants in the effluent in mg/1 and measurement of
the effluent discharge rate in 1/hr. Expressing the effluent
limitation as a function of a production unit compensates for
change in production rate, which changes the effluent discharge
rate. The effluent rate in the electroplating industry is
closely related to the rinse water rate which is in turn related
to the production rate of electroplated parts.
The effluent discharge rate as volume per day is commonly
reported by electroplating and other industrial sources. Because
many plants do not work on a 24-hour-day basis at all times, it
would be preferable to use the next smaller unit of time, which
is an hour. This avoids the uncertainty associated with the
daily unit which often requires further defintion as to the
number of shifts worked per day and the hours per shift.
The most appropriate production unit in some industries is the
weight of product produced or the weight of raw materials
purchased. Niether a unit quantity of product produced nor a unit
quantity of raw material use is appropriate for the
electroplating industry, because the quantity of product
expressed as the weight of products plated does not bear any
relation to raw waste produced. Electroplating is a surface
process that is not influenced by the volume or density of the
part plated. The raw waste load is related to surface area (not
volume) of electroplated parts which determines the concentrated
solution dragout, rinse water use, and ultimately the degree of
pollution reduction achievable. While it is common in barrel
plating of small parts to weigh the plated parts as a control
measure for basket loading, the optimum weight of parts was
originally determined by trial and error plating or
precalculation of the part per unit weight in order to achieve
the correct total area for optimum plating current density.
Regardless of the method of controlling the plating operation,
the dragout is related to the total area of parts plated and not
the weight. Solution adhering tc the surface of small parts
causes dragout. Although some cup-shape parts that are difficult
to drain or rinse may cause high dragout not directly related to
area, weight would not be a good unit quantity applicable to both
rack and barrel plating.
Although the amount of raw material used or chemicals purchased
was considered as a possible unit quantity related to production,
neither unit appeared suitable as a reliable measure of
production. The weight of material purchased and used as soluble
anodes ends up on the parts plated, but this weight must be
divided by the thickness plated to obtain a correlation with
production rate in area plated per unit time which is the true
determinant of raw waste load. In the case of chemicals
purchased for bath make up and particularly for chromium salts
172
-------
purchased for plating with insoluble anodes, there is a further
complication. A material balance will show that the difference
between the chromium purchased and the chromium on the plated
parts produced equals the chromium in the precipitated sludge
minus the small amount of chromium discharged with the treated
effluent. Thus, chromium in chromium salts purchased in excess
of that on plated parts reflects dragout and increased sludge but
not necessarily increased water pollution. The same reasoning
applies to all other metal-containing chemicals purchased for
bath make up which primarily end up as precipitated and separated
sludge. Although the amount of chemicals purchased indicates
total dissolved salts in the treated effluent, total dissolved
solids is not considered an important pollutant parameter in the
electroplating industry.
Consideration of the above factors led to the conclusion that the
unit of production most applicable to the electroplating industry
is surface area. The surface area withdrawn from a concentrated
solution in a plating operation is the paramount factor
influencing dragout of solution constituents, some portion of
which ends up in the waste water and treated effluent. Surface
area influencing dragout includes not only the surface area
receiving an electroplate but 'also the surface area of
nonsignificant surfaces receiving little or no electrodeposit
plus the surface area of racks or barrels which hold the parts.
The total surface area is rarely known and impractical to measure
in some cases in the electroplating industry. In this case, the
plated area is the alternative logical unit of production.
However, plated area is not a measurement that has been
historically recorded by the industry and may not be readily
available from all plants. Alternative units of production based
on amperes and water use, which are more easily measured, were
developed and correlated with plated area and ultimately to the
total surface area in establishing effluent limitations. These
alternatives means of calculating the area plated should only be
used until the industry does have ample records of area plated.
Plated Area Unit of Production*
The plated area is the primary unit of production on which the
effluent limitations in Table 1 are based. Plated area is
defined with reference to Faraday's Law of electrolysis by the
following equation:
-MS Equation 2
S = 100 kt
where S = area, sq m (sq ft)
E = cathode current efficiency, percent
I - current used, amperes
T = time, hours
t = average thickness of deposit, mm (mil)
k - a constant for each metal plated based on
the electrochemical equivalent for metal
173
-------
deposition, amp-hr/mm-sq m (amp-hr/mil-sq ft),
The numerical product of current and time (IT) is the value that
would be measured by an ampere-hour meter. Values of the
constant k based on equivalent weight and the valence of the
metal deposited are shown in Table 35.
Average thickness can be approximated by averaging thickness
measurements at several points on a single plated part, to
establish the ratio of average to minimum thickness. Minimum
thickness is customarily monitored to meet the specifications of
purchasers of electroplated parts, based on service requirements.
This equation was used in this study to determine the plated
areas per unit time in each plating operation when the only
available information was the current used and the average
thickness of deposit. This equation was also used as a check on
estimates of surface area plated provided by the plants
contacted.
To calculate the total plated area on which the effluent
limitations are based for a specific plant, it was necessary to
sum up the area for each electroplating process line using
Equation (2) . For process lines containing two or more
electroplating operations (such as in copper-nickel-chromium
decorative plating) the plated area is calculated by Equation (2)
for each plating operation in the process. The results should be
the same, since the same parts are processed through each
operation. However, if the calculated plated area differed for
each plating operation in a single process line, the average of
the calculated plated areas for the operations was used. The sum
of the plated areas for each process line is the total plated
area for the plant.
Small dlscrepencies in the above calculation for two or more
plating operations in the same process line might be related to a
difference in the actual current efficiencies from those in Table
36 which are to be used for the calculation. However, experience
with data from several plants indicated that the more likely
cause of the discrepancy is the accuracy of the reported values
of average plate thickness.
The use of ampere-hour on rectifiers might have value for
monitoring or record keeping for some plants in lieu of measuring
the area of the parts plated provided the average thickness
plated is known or determined.
Records of plating voltage and ampere-hours on each rectifier (or
watt-hours) plus thickness deposited might be correlated with
watt-hours of electricity consumed per day or month with
allowance for other electricity uses (lighting, pumps, etc) to
estimate total plated area per day or month. The total effluent
could be approximated by the plant water purchases if mainly for
electroplating. Thus, the information on electric power
consumption and water consumption from monthly bills for these
*The Guidebook and Directory for Metal Finishing (3 ) p. 426-429
gives a detailed description of methods for calculating area
plated.
174
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TABLE 3t> TYPICAL CURRENT EFFICIENCIES ASSUMED
FOR CALCULATION OF PLATED AREA
USING EQUATION (2)
Type of
Plating Operation
Typical
Current
Efficiency, Constant(k}
percent ainp-hr/mm-sq m amp-hr/mil-sq ft
Cyanide copper
Noncyanide copper
Nickel
Chromi urn
Cyanide zinc
Noncyanide zinc
50 3.75 x 103
100 7.49 x 103
100 8.05 x 103
13 21 .95 x 103
60 5.80 x TO3
100 5.80 x 103
8.84
17.68
19.00
51 .80
13.70
13.70
175
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services might be used in an approximation of daily plated area
for a cross check against plated area determined by more direct
means.
In practice, it should be possible for electroplaters to readily
adapt to keeping records of plated area for reporting purposes.
The fact that many platers do not presently know their production
rate in terms of surface area plated is not a valid consideration
since there has been no prior requirement to keep such records.
Determining plated area should not be difficult for platers whose
process operation is dependent on use of the correct current
density for optimum plating results.
Total surface area is more closely related to dragout than plated
area, and can generally be estimated once the plated area is
known. If a part is plated on only one side the total surface
area would be approximately twice the plated area. In barrel
plating total surface area would be the same as plated area.
Application of Guidelines
Definition of Terms
To discuss the application of the guidelines it is first
necessary to define several terms.
"process";
"Operation";
A process is the accumulation of steps
required to bring about a metal finishing
result. An electroplating process
includes cleaning and usually pickling
of the basis metal, a strike if
necessary, the plating step, and all
rinses needed to carry out the process.
The term operation shall mean any step
in the plating process in which copper,
nickel, chromium, or zinc metal or
chrornate is deposited on a base
material followed by a rinse. The
processing steps of cleaning and
pickling are not operations,
A rinse is a step in a process used to
remove components of a bath from the
work following an operation. A rinse
may consist of a sequence such as
successive countercurrent rinsing
or hot rinsing followed by cold rinsing
with deionized water. Nevertheless,
there is only one rinse after an
operation,
In determining the allowable discharge of a pollutant, it is
important to be able to count the number of operations in a
"Rinse";
176
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process. In the following process there are two operations
marked with asterisks.
Alkaline Clean
Rinse
Acid Dip
Rinse
* Nickel Plate
Rinse
* chromium Plate
Rinse
The alkaline cleaning and acid dip steps are not operations even
though they are followed by rinses. In effect, the rinse waters
from these operations are considered a part of the rinse water
following the first plating step (Nickel Plate) In considering
water use.
In the following process the copper strike is not an operation
since it is not followed by a rinse.
Alkaline Clean
Rinse
Copper Cyanide strike
* Copper Cyanide Plate
Rinse
Copper cyanide plating is the only operation.
Determination of _Plated Area/Hr/Operatipn
The area for each line will be determined from information on the
(1) average amperes used, (2) the sequence of plating operations,
and (3) the average thickness in mil of each type of plate, If
complete data on thickness is lacking, the following value will
be used:
Copper 0.3 mil
Nickel 0.3 mil
Zinc 0.3 mil
Chromium 0.015 mil
Where chromating follows plating, the area will be the same as
that of the primary plating operation. The equation:
S = EIT/1QO kt (see page 173}
is then used to calculate plated area/hr/operation. In a line
with several sequential operations, it is likely that the
calculated plated areas for each plating operation will vary from
each other although the actual area plated should be the same.
The difference in calculated areas many vary by a factor of two
or three. When applying the guidelines the figure used for area
plated should be the arithmetic average of the calculated plated
areas.
177
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where actual amperes are not known a value equal to 2/3 of the
installed capacity for the line should be used. Where
inflation X amperes is completely lacking for a line but water
use is available, the sq m/hr may be determined by:
Sq m/hr = 1/hr used on the line
C200 1/sq m) (no. of operations )
Sq ft/hr = gal/hr used on the line
(5 gal/hr) (no. of operations )
Once the plated area has been measured the guidelines can be used
to determine the total allowable discharge of waste water
constituents from the plant. Every time the surface is rinsed,
flowing some operation in the process line, it is assumed that
more was?e water is produced, and a greater quantity of waste
water constituents *«ay be discharged under the guidelines. The
cleaning and pickling rinses are therefore incorporated into the
rinse following the first plating operation for purposes of
SlcSlalSg^ allowable amount of waste water constituents
discharged! The total allowable discharge in g/day will be:
(10-3) (sq m plated /hr) (effluent limitation in mg/sq m)
(No. of oper. ) (hr/day)
The total allowable discharge in Ib/day is:
(10-6) (sq ft plated/hr) (effluent limitation 1K/,a,,
in Ib/million sq ft (No. of oper. ) (hr/day) = Ib/day
These relations hold for each effluent
valuP listed in Table 1. The relations apply to each process
UnT or Jart of a process line if the area plated ./hr changes
in the line.
The actual discharge from the plant is the product of the volume
of effluent/hr and the concentration of waste water constituent
in the effluent.
Thus,
g/day = (liters/hr) (mg/1) (10-*) (hr/day)
Ib/day = (8.33 x 10-«) (gal/hr) (mg/1) (hr/day)
Several examples will show how the guidelines are applied to
specific processes.
Example 1. A process line is shown in Figure 33. The process
consists" of zinc plating on steel followed by chromating. The
line plates an estimated 10 sq m/hr (107.6 sq ft/hr) of work and
operates 8 hours/day. For purposes of this example, the plant
will be considered to have only the one zinc plating line.
Effluent volume from the waste treatment system is 1000 1/hr (264
gph) . concentrations of waste water constituents in the effluent
are
Zinc 1-0
178
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Vapor
Degrease
Alkaline Clean
Rinse
Acid,Dip
Rinse
Zinc Plate
Rinse
Chromate
Rinse
Dry
FIGURE 33 PROCESS LINE FOR EXAMPLE 1
179
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Cyanide (total) 0.6 mg/1
Cyanide (oxidizable) 0.03 mg/1
Chromium (heKavalent) 0.05 mg/1
Chromium (total) 1.2 mg/1
TSS 15,
For purposes of calculating amount of discharge, the alkaline
clean and acid dip steps are not counted; the zinc plating and
chromating operations are counted to give a total of two.
Allowable Zn discharge = (2.04 x 10~6)(107.6) (16.a) (2) (8)
= 2.82 x 10-2 Ib/day
Actual Zn discharge = (8.33 x 10~6) (264) (1.0)
= 2.19 x 10~3 Ib/hr
= (2. 19 x 10-*) (8)
= 1.76 x 10-2 Ib/day.
Effluent discharge for 8 hours is assumed. However, a composite
sample taken over a different time span, i.e., 24 hours can be
used to establish effluent concentrations and an average flow for
the same time used. Therefore, the actual discharge of zinc is
within the allowable limit. .Allowable and actual limits for
other waste water constituents are calculated in an identical
manner. Results are as follows:
Allowable Discharge, Actual Discharge,
Constituent Ib/day __ ______lb/da^; ^___
Zinc 2.82 x 10-2 1.76 x 10«2
Cyanide (total) 2.82 x 10~2 1.06 x 10~*
Cyanide (oxidizable) 2.82 x 10-* 5.28 x 10-*
Chromium (hexavalent) 2.82 x 10~3 8.79 x 10-*
Chromium (total) 2.82 x 10~* 2.11 x 1Q-*
TSS 1.13 8.43 x 10~»
The effluent limitation guidelines are all met in this example
since all actual discharges are below allowable discharges.
Example 2. A process line is shown in Figure 34. The process
consists of plating steel with copper, nickel, and chromium. The
line processes an estimated 20 sq m/hr (215 sq ft/hr) of work and
operates 1.6 hours/day. For purposes of this example, the line
will be considered the only one in the plant. Effluent volume
from the waste treatment system is 6000 1/hr (1585 gph).
Concentrations of waste water constituents in the effluent are:
Copper 0.5 mg/1
Nickel 1.3 mg/1
Chromium (hexavalent) 0.05 mg/1
Chromium (total) 1.2 mg/1
Cyanide (total) 0.6 mg/1
Cyanide (oxidizable) 0.03 mg/1
TSS 15.
180
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Alkaline Clean
Rinse
Copper Strike
Copper Plate
Rinse
Nickel Plate
Rinse
Chromium Plate
Rinse
Dry
FIGURE
34
PROCESS LINE FOR EXAMPLE 2
181
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Note in Figure 34 that there is an alkaline cleaning, but no acid
pickle. Thus, only the rinse after the alkaline cleaning step is
omitted in counting operations. There is no rinse following the
copper cyanide strike, and therefore this operation is not
counted. The copper cyanide plating, nickel plating, and
chromium plating operations have following rinses and are counted
to give a total of three operations.
Allowable Cu discharge = (1Q~6) (215) (16.4) (3)
= 1.05 x 10-2 ib/hr
= (1.05 x 10-2) (16)
= 0.168 Ib/day
Actual Cu discharge = (8.33 x 10-*) (1585) (0.5)
= 6.60 x 10-3 Ib/hr
= (3.30 x 10-3) (16)
= 0. 105 Ib/day.
Effluent flow for 16 hours a day is assumed, but a similar
calculation can be made for values of concentration and flow
average over 24 hours.
Therefore, the actual discharge of copper is within the allowable
limit. Allowable and actual limits for other waste water
constituents are calculated in an identical manner. Results are
as follows:
Allowable discharge. Actual discharge,
n
Copper 0.168 0.105
Nickel 0.168 0.274
Chromium (hexavalent) 0.0168 0.0105
Chromium (total) 0.168 0.253
Cyanide (total) 0.168 0.126
Cyanide (oxidizable) 0.0168 0.006
TSS 6.74 3.16
In this example the guideline is exceeded by nickel and total
chromium.
Example 3. This example will consider a plant made up of the
line used in Example 1, plus the line used in Example 2. The
effect of combining these two lines is to increase the allowable
and actual discharge of constituents that originate in only one
line. The reason for the increases is that the waste waters from
both lines are brought together before final precipitation and
clarification. Therefore, copper and nickel contaminate the
waste water from the zinc plating line, and zinc contaminates the
waste water from the copper-nickel-chrome line. The effect of
the mutual dilution is to produce as much zinc discharge as if
all waste water came from the zinc line, and as much nickel and
copper discharge as if all waste water came from the copper-
nickel-chrome line. Since chromium is a waste water constituent
from both lines, the total discharge of this constituent is
182
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merely the sum of -the effluent discharge from the separate lines.
The statement is true -he mutual dilution effect is not
sufficient to bring the concentration of the waste water
constituent below the value that can be obtained by
precipitation. Normally, a 50- to 100-fold or greater dilution
must be made which is unlikely where water conservation is
practiced,
Where waste water from more than one line is combined, the waste
water volume from each line is often not known, but only the
total effluent volume. This will be 1,000 1/hr from the zinc
line for 8 hours a day and 6,000 1/hr from the Cu-Ni-Cr line for
16 hours a day. Assume that the waste treatment plant operates
16 hours a day with effluent drainage of 6,500 1/hr (1717 gph).
Concentrations of waste water constituents in the effluent are;
Zinc 1.0 mg/1
Copper 0.5 mg/1
Nickel 1.3 mg/1
Chromium (hexavalent) 0.05 mg/1
Chromium (total) 1.2 mg/1
Cyanide (total) 0.6 mg/1
Cyanide (oxidizable) 0.03
TSS 15.
The calculations for zinc are:
Allowable Zn discharge = [ (10-*) (16.4) ] [ (107.6) (2) (8) +
(215) (3) (16) ] = 0.197 Ib/day
Actual 2n discharge = (8.33 x 10-*)(1717)(1.0)(16) = 0.228
In the first calculation the result is the same as though zinc
were plated on the second line rather than Cu-Ni-Cr since it
makes no difference whether the zinc came from the plating
operation or through contaminants of waste water from line 2 by
zinc-containing waste water from line 1. The calculation assumes
that after the zinc plating line has operated for 8 hours and is
turned off, zinc contamination of the waste water from the Cu-Ni-
Cr line continues for the additional hours that this line
operates. This assumption is valid as long as the contamination
exceeds the effluent concentration of 1.0 mg/1 of zinc. The
allowable discharge for zinc is exceeded when the two lines are
combined in Example 3, while the zinc line operating by itself
(Example 1) is able to stay within discharge limits. The larger
water use per sq m in the Cu-Ni-Cr line is responsible for this
difference. The results for other constituents may be summarized
as follows:
Constituent
Zinc
Copper
Allowable Discharge Allowable Discharge
for single line for combined lines
Ib/day
0.0280
0.108
Actual Discharge
for combined lines
0.197
0.197
.228
183
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Nickel 0.168 0.197 .297
Chromium
(hexavalent) 0.00280/.0168 0.020 .011
Chromium
(total) 0.0280/0.168 .0.197 .275
Cyanide
(total) 0.0280/0.168 0.197 .137
Cyanide
(oxidizable) 0.00280/.0168 0.020 ,006
TSS 1.13/674 7.88 3.43
Discharge from the combined lines exceeds the allowable amounts
for zinc, nickel, and total chromium.
Example 4_. Example 4 is that of a line that splits its
operations at a point in the process. Thirty sq m/hr (323 sq
ft/hr) are processed through the copper strike and plate. Twenty
sq m/hr (215 sq ft/hr} are processed through semi-brite nickel
and eventually through chrome plating. Ten sq m/hr (107»6 sq
ft/hr) go directly from the copper plate rinse to brite nickel
and chrome plate. The line operates 24 hours/day. The allowable
discharge from this line is:
(10~6) [(323) (1) H- (2155(3) + (107.6) (2)] (24) (ELG) = Ib/day
where ELG is the effluent limitation guideline for the
specific waste water constituent. The '323 sq "£t/hr of an
operation go through one operation, copper plating. The 215 sq
ft/hr go through three operations, and the 107.6 sq ft/hr go
through three operations.
For copper:
(lo" ) (16.4) (24) [(323) (1) -I- (107.6) (2) + (215) (3)] = .465 Ib/day
Allowable Discharge,
Constituent Ib/day ___
Copper 0.-465
Nickel 0.465
Chromium (hexavalent) 0.0465
Chromium (total) 0.465
Cyanide (total) 0 .,-
Cyanide (oxidizable) o;JJ|s
TSS
184
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Actual discharges are the product of effluent flow, and
concentration, as in previous examples.
185
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Alkaline Clean
Rinse
Pickle
Rinse
Copper Strike
JL
Brite Nickel
Copper Plate
Rinse
Semi Brite Nickel
Rinse
Chrome Plate
Rinse
Dry
Rinse
Brite Nickel
Rinse
Chrome Plate
Rinse
Dry
FIGURE -35 PROCESS LINE FOR EXAMPLE 4
186
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SECTION X
BESf AVAILABLE TECHNOLOGY gCQNOMICM.LY
ACHIEVABLEf SOIDEflNES AND LIMITATIONS
The effluent limitations which must be achieved by July 1, 1983
are to specify the degree of effluent reduction attainable
through the application of the Best Available Technology
Economically Achievable, This technology can be based on the
very best control and treatment technology employed by a specific
point source within the industry category and/or subcategory or
technology that is readily transferable from one industry process
to another. A specific finding must be made as to the
availability of control measures and practices to eliminate the
discharge of pollutants, taking into account the cost of such
elimination.
Consideration must also be given to;
(a) the age of the equipment and facilities involved;
(b) the process employed;
(c) the engineering aspects of the application of various
types of control technologies;
(d) process changes;
(e) cost of achieving the effluent reduction resulting from
the technology;
(f) nonwater quality environmental impact (including energy
requirements).
The Best Available Technology Economically Achievable also
assesses the availability in all cases of in-process controls as
well as the control or additional treatment techniques employed
at the end of a production process.
A further consideration is the availability of processes and
control technology at the pilot plant, semi-works, or other
levels, which have demonstrated both technological performances
and economic viability at a level sufficient to reasonably
justify investing in such facilities. Best Available Technology
Economically Achievable is the highest degree of control
technology that has been achieved or has been demonstrated to be
capable of being designed for plant scale operation up to and
including no discharge of pollutants. Although economic factors
are considered, the costs for this level of control are intended
to be top-of-the-line of current technology subject to
limitations imposed by economic and engineering feasibility.
187
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However, Best Available Technology Economically Achievable may be
characterized by some technical risk with respect to performance
and with respect to certainty of costs and thus may necessitate
some industrially sponsored development work prior to its
application.
Industrv^CateggrgandSubcategorv_Cgvered
The pertinent industry category is the electroplating industry as
defined previously in Section IX.
Identification,of Best Available Technology.
IcoDomical ly Jkchi evajble
The Best Available Technology Economically Achievable is the use
of in-process and end-of-process control and treatment to achieve
no discharge of pollutants. By the use of in-process controls to
reduce the volume of wastewaterr it becomes economical to use
end-of-process treatment designed to recover water and reuse the
water within the plant thus avoiding any discharge of effluent to
navigable waters. Solid constituents in the wastewater are
disposed of to landfill or otherwise. As discussed in Sections
VII and VIII one such type of treatment system that has been
designed and is currently in operation supplements conventional
chemical treatment with the use of reverse osmosis to recover
water from the treated waste stream. Additional water is
recovered for reuse by evaporation and distillation of the
concentrated waste stream from the reverse osmosis unit. The
concentrated wastewater solution from the evaporator is dry salt.
It is expected that other methods will be developed during the
next five years to avoid discharge of effluent to navigable
waters and thus achieve no discharge of pollutants in an
economical manner.
Rationale for selection ofBest Available
Technology Economically Achievable
Time Available for Achieving Effluent Limitations
As noted previously, the effluent limitations selected for the
Best Available Technology Economically Achievable for existing
sources do not have to be achieved before July 1, 1983. This
longer-range limitation allows sufficient time for retirement and
replacement of existing electroplating and waste-treatment
facilities as needed. Not all of these necessary changes can be
expected by July 1, 1977 without placing an unjustifyable
economic burden on -those plants which are currently practicing
pollution abatement.
Age of Equipment and Facilities
188
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Replacement of older electroplating equipment and facilities will
permit the installation of modern inultitank countercurrent
rinsing systems after each operation in each process line with
conservation of water use for rinsing. The use of reclaim and
recovery systems after each plating operation should be possible.
Use of in-process controls to the maximum extent will reduce the
volume of effluent such that recovery and reuse of water is
economically attractive.
Process Employed
The application of the technology for end-of-process recovery and
reuse of water to the maximum extent possible is not dependent on
any significant change in the processes now used in the
electroplating industry. Most water recovery technology can
produce a higher quality of water than normally available from
public or private water supplies. High purity water for the
final rinse after plating is desirable to improve the quality of
the electroplated product.
Engineering Aspects of the Application of Various Types of
Control Techniques
Many plants are successfully using evaporative recovery systems
after one or more plating operations with a net savings compared
to chemical treatment. Evaporative systems are in current use
after copper, nickel, chromium and zinc plating operations. Some
plants have succeeded in using recovery systems after all plating
operations in their facility. The engineering feasibility of in-
process controls for recovery of chemicals and reuse of water are
sufficiently well established. Sufficient operational use has
been accumulated to reduce the technical risk with regard to
performance and any uncertainty with respect to costs.
The technical feasibility of end-of-process water recovery
systems has been established by extensive development of the
recovery of pure water in many related industrial processes.
Although some uncertainty may remain concerning the overall costs
when applied to electroplating wastewaters, such uncertainty
primarily relates to the volume of water that must be processed
for recycling and reuse. The fact that the technology as applied
to the electroplating industry has progressed beyond the pilot
plant stage and has been designed and is being built for full-
scale operational use indicates that the technology is available
and probably economical.
Process Changes
Application of the technology is not dependent on any process
changes. However, process changes and improvements are
anticipated to be a natural consequence of meeting the effluent
limitations in the most economic manner.
189
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Cost of Achieving the Effluent Reduction
The costs of achieving no discharge of pollutants from large
facilities electroplating copper, nickel, chromium, and zinc are
expected to be no greater than $17.20/100 sq m ($16.00/1,000 sq
ft) as discussed in Section VIII. With lower cost techniques,
the cost for achieving no discharge of pollutants may be about
the same as the cost for conventional chemical treatment, which
averages about $10.70/100 sq m ($9.91/1,000 sq ft). The cost
range for achieving no discharge of pollutants is expected to be
only 4 to 6.5 percent of the plating costs. It may be possible
to recover and reuse sufficient chemicals and water to offset the
costs of achieving no discharge of pollutants in some plants.
Cost for small plants of achieving no discharge of wastewater
pollutants to navigable waters are greater than $17.20/sq ft
($16.00/1,000 sq ft) as indicated in Table 22, Costs for small
plants increase as size decreases because there is a minimum
capital investment for equipment required to achieve reuse of
water.
Nonwater Quality Environmental Impact
Application of technology to achieve no discharge of wastewater
pollutants to navigable waters by July 1, 1983, will have little
impact on the solid waste disposal problem with regard to metal
removal as sludge beyond that envisioned to meet effluent
limitations recommended for July 1, 1977.
In general, it is anticipated that the technology will be applied
in a manner such that no discharge of effluent to surface waters
occurs. Thus, all of the dissolved solids in the effluent which
are primarily innocuous salts would be disposed of on land with
suitable precaution to avoid any ground water contamination.
Because these salts are not large in amount and can be dewatered
to dry solids (by incineration if necessary) very little
additional impact on the solid waste disposal problem is
anticipated.
No impact on air pollution is expected as the result of achieving
no discharge of pollutanzs to surface water. The available
technology creates no air pollutants.
Energy requirements will increase with the achievement of no
discharge of pollutants to surface water. The amount will vary
from about 27 percent of the energy consumed by electroplating
sources to as much as four times the energy needed for plating,
depending on the specific process controls adopted in individual
plants for achieving no discharge of pollutants.
gf£luent:=LLimitatigns Based on the Application
of Best,Available Technglocry EconomicallyT Achievable
The recommended effluent limitations to be achieved by July 1,
1983 for existing sources based on the application of Best
190
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Available Technology Economically Achievable is no discharge of
wastewater pollutants to navigable waters.
Guidelinesfor the Application of
Efjrluent Limitations
Achieving the effluent limitations of no discharge of wastewater
pollutants by achieving no discharge of effluent to surface
waters is the most direct method that eliminates the need for
sampling and analysis. If there is other effluent discharge to
surface waters from the plant not associated with electroplating,
a determination is required that no wastewaters originating from
electroplating processes are admixed with this other plant
effluent.
191
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SECTION XI
NEWSOURCEPERFORMANCE^STANDARDS
Introduction
The standards of performance which must be achieved by new
sources are to specify the degree of effluent reduction attain-
able through the application of higher levels of pollution
control than those identified as Best Available Technology
Economically Achievable for existing sources. The added con-
sideration for new sources is the degree of effluent reduction
attainable through the use of improved production processes
and/or treatment techniques. The term "new source" is defined by
the Act to mean "any source, the construction of which is
commenced after publication of proposed regulations prescribing a
standard of performance".
New Source Performance Standards are based on the best in-plant
and end-of-process technology identified as Best Available
Technology Economically Achievable for existing sources.
Additional considerations applicable to new source performance
standards take into account techniques for reducing the level of
effluent by changing the production process itself or adopting
alternative processes, operating methods, or other alternatives.
The end result will be the identification of effluent standards
which reflect levels of control achievable through the use of
improved production processes (as well as control technology),
rather than prescribing a particular type of process or
technology which must be employed, A further determination must
be made as to whether a standard permitting no discharge of
pollutants is practicable.
consideration must also be given to:
(a) the type of process employed and process changes
(b) operating methods
(c) batch as opposed to continuous operations
(d) use of alternative raw materials and mixes of raw
materials
(e) use of dry rather than wet processes (including
substitution of recoverable solvents for water)
(f) recovery of pollutants as by-products.
Standards of Performance for New Sources are based on applicable
technology and related effluent limitations covering discharges
directly into waterways.
Consideration must also be given to the fact that Standards of
Performance for New Sources could require compliance about t;hree
years sooner than the effluent limitations to be achieved by
existing sources by July 1, 1977, However, new sources should
achieve the same effluent limitations as existing sources by July
1, 1983.
193
Preceding pap blank
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Industry ^Category _and_ Sybcat-ggory^Covered
The recommended new source performance standards cover the
electroplating industry category as previously defined in Section
IX,
Control and Treatment
The technology previously identified in Section IX as Best
Practicable Control Technology Currently Available is also
applicable to New Source Performance Standards. In addition a
new source can utilize the best practice in multitank rinsing
after each operation in the process as required to meet the
effluent limitations at the time of construction. Thus, with no
practical restrictions on rinsewater conservation after each
operation by multitank rinsing, there are fewer restrictions on
the use of advanced techniques for recovery of plating bath
chemicals and reduction of wastewater from rinsing after pre-
treatment and post treatment. Maximum use of combinations of
evaporative, reverse osmosis, and ion exchange systems for in-
process control currently available should be investigated. A
small end-of-pipe chemical treatment system can be used to treat
spills, concentrated solution dumps, and any other water flows
not economically amenable to in-process water and chemical
recovery.
The technology previously identified in Section X as Best
Available Technology Economically Achievable is also applicable
to New Sources to achieve zero discharge of pollutants to
navigable waters at least by July 1, 1983, as required for
existing sources.
Rationale for Selection of Control and
Treatment^ Technology^ ABElicable_to
jew Source .......... Performance .Standards ""
The rationale for the selection of the above technology as
applicable to new sources discharging to navigable waters is as
follows:
(1) In contrast to an existing source, a new source
has complete freedom to choose the most advan-
tageous electroplating equipment and facility
design to maximize water conservation by use of
as many multitank rinsing operations as necessary.
This, in turn, allows for economic use of in-
process controls for chemical and water recovery
and reuse.
(2) In contrast to an existing source which may have at
194
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present a large capital investment in waste treat-
ment facilities to meet effluent limitations by
July 1, 1977, a new source has complete freedom in
the selection of the Best Available Technology
Economically Achievable in the design of new waste
treatment facilities.
(3) In contrast to an existing source, a new source has
freedom of choice with regard to geographic location
in seeking any economic advantage relative to power
cost or land cost.
Since the technology for achieving no discharge of pollutants has
been demonstrated to be capable of being designed to achieve no
discharge of effluent for a facility recently constructed, it is
considered the best demonstrated technology currently available
for some new sources. The possibility of a slightly .higher cost
in relation to several orders of magnitude reduction in pollution
and the possible elimination of monitoring expense for no
discharge of effluent warrants selection of this technology in
defining the standard of Performance for the electroplating
industry to be achieved by July 1, 1983.
Consideration was given to the other factors listed in the
Introduction to this section pertinent to defining the control
and treatment technology applicable to New source Performance
Standards, Based on informa-tion developed in Sections III
through x of this report, it is evident that there are many more
advantageous options available to a new source, relative to those
available to an existing source. Thus a new source should
achieve greater pollution reduction.
Standards of Performance
Sources
The recommended standards of Performance to be achieved by new
sources discharging to navigable waters was shown previously in
Table 2 of Section II.
The quantitative values for the 30-day average standard for each
parameter in mg/sq m (lb/106 sq ft) is based on a nominal
effluent factor of 80 1/sq m (1 gal/sq ft) combined with the
concentrations achievable by chemical treatment as previously
shown in Table 3H of Section IX for existing sources based on an
effluent factor of 80 1/sq m. For example, 0.5 mg/1 for copper,
nickel, total chromium, zinc, and total cyanide, 0.05 mg/1 for
hexavalent chromium and oxidizable cyanide, 15 mg/1 for suspended
solids, when combined with an effluent factor of 80 1/sq m are
the basis for the 30-day average standards of performance in
Table 2.
In effect, standards of Performance for New Sources Table 2 are
one half the values of the Effluent Limitations for existing
sources to achieve by July 1» 1977, as shown in Table 1, The
rationale for selection of Standards of Performance is based on
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the technical feasibility of achieving greater reduction in water
use by multitank rinsing at the time of construction of new
facilities in contrast to the present limitations for some
existing sources. For example, if an existing source can achieve
an effluent factor of 160 1/sq m, a new source should be able to
design a new facility to achieve an effluent factor of 80 1/sq m.
As discussed previously in Section IX, the Standard of
Performance in mg/sq m is the product of the plant effluent
factor in 1/sq m and the concentration of the parameter in the
treated effluent in mg/1. The choice of whether to reduce
concentration by emphasis on optimum chemical treatment and
clarification or whether to reduce effluent volume by water
conservation or a combination of both approaches is left to the
discretion of the new source.
The rationale for establishing the daily maximum value of
Standards of Performance at twice the 30-day average is based on
the limitations in accuracy of analytical methods for measuring
small concentrations, the usual 24-tirne lag after analysis for
corrective action, the accuracy of measurement of effluent flow,
and plated areas as discussed previously in Section IX.
It is recommended that new sources meet the same effluent
limitations as required for existing sources by July 1, 1983,
based on the effluent reduction believed to be attainable by the
application of the Best Available Technology Economically
Achievable.
Guidelines for the ApBlicatiQn of
New Source Performance Standards
The recommended guidelines for the application of Standards of
Performance for New Sources discharging to navigable waters are
the same as those in Section IX relating to existing sources
based on use of the Best Practicable Control Technology Currently
Available and those in Section X based on use of Best Available
Technology Economically Achievable.
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SECTION XII
ACKNOWLEDGEMENTS
The Environmental Protection Agency was aided in the preparation
of this Development Document by Battelle Columbus Laboratories
under the direction of William H. Safranek, Luther Vaaler, Jack
Clifford, John Gurklis and Carl Layer on Battelle"s staff-made
significant contributions.
Harry M. Thron, Jr. served as project officer on this study
through the initial work with the contractor and development of
the proposed document. His work was invaluable to the successful
completion of the final document. Allen Cywin, Director,
Effluent Guidelines Division, Ernst P. Hall, Deputy Director,
Effluent Guidelines Division and Walter J. Hunt, Chief, Effluent
Guidelines Development Branch, offered guidance and suggestions
during this program.
The members of the working group/steering committee who
coordinated the internal EPA review are;
Allen Cywin, Effluent Guidelines Division
Walter J. Hunt, Effluent Guidelines Division
Harry M. Thron, Effluent Guidelines Division
Kit R, Krickenberger, Effluent Guidelines Division
Edward Dulaney, Effluent Guidelines Division •
Murray Strier, Office of Permit Programs
John Ciancia, NERC, Cincinnati, (Edison)
Hugh Durham, NERC, Corvallis (Grosse lie)
Lew Felleison, Region III
Tom Gross, Office of Solid Waste Management Programs
Tim Fields, Office of Solid Waste Management Programs
Alan Eckert, Office of General Counsel
Swep Davis, Office of Planning and Evaluation
Acknowledgement and appreciation is also given to the secretarial
staff of both the Effluent Guidelines Division and Battelle for
their effort in the typing of drafts and necessary revisions, and
the final preparation of this document:
Kaye Starr, Effluent Guidelines Division
Nancy Zrubek, Effluent Guidelines Division
Linda Rose, Effluent Guidelines Division
Brenda Holmone, Effluent Guidelines Division
Chris Miller, Effluent Guidelines Division
Sharon Ashe, Effluent Guidelines Division
Nancy Dunn, Battelle
Paula Thompson, Battelle
Terri Floyd, Battelle
197
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Appreciation is extended to the following organizations
associated with the electroplating industry:
.American Electroplaters Society
duPont de Nemours and Company
Hell Process Equipment Corporation
Industrial Filter and Pump Manufacturing Company
Ionic International, Inc.
Lancy Laboratories
M and T Chemicals, Inc.
Metal Finishing Suppliers' Association, Inc..
National Association of Metal Finishers
Osraonics, Inc.
Oxy Metal Finishing Corporation
The Permutlt Company
Pfaudler Syhron Corporation
198
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SECTION XIII
REFERENCES
(1} Safranek, M. H., "The Role of Design in Better Plating",
Metal Progress, pp 67-70 (June 1968}.
(2) Jtodern §1ectrpplating, Edited by F. A. Lowenheim,
Second Edition, John Wiley and sons (1963), Chapter 7,
pp 154-205.
(3) M,etajL Finishing Guidebook and Directory, Metals and
Plastics Publications,~fnc7 (1973).
(4) "Methods for Chemical Analysis of Water and Wastes",
Environmental Protection Agency, Water Quality Office,
Cincinnati, Ohio (July 1971).
(5) Standard Methods for the Examination of Water and
Wastewater, Thirteenth Edition (1971). ~
(6) ASTM Designation 2036-72.
(7) Ceresa, M., and Lancy, L. E., "Metal Finishing Waste
Disposal. Part One", Metal Finishing, 66 (4), 56-62
(April 1968) .
(8) Pourbaix, Marcel, Atlas of Electrochemical gguilibria
iii Agueous Solutions, Pergamon Press, New York (1966) .
(9) Marquardt, Kurt, "Erfahrungen mit lonensautauschern
als Endreinungsstufe nach Entgiftung- und Neutralisation-
sanlagen aller Art", Metalloberflache Angew. Elektro-
chemie 26 (11) , H3H (1972) .
(10) Personal communication from Dr. Coleman, Western
Electric Company, Indianapolis, Indiana.
(11) Environmental Sciences, Inc., "Ultimate Disposal of
Liquid Wastes by Chemical Fixation™.
(12) Tripler, A. B., Cherry, R. H., Smithson, G. Ray,
Summary Report on the Reclamation of Metal Values from
Metal Finishing Waste Treatment Sludges", Battelle
Columbus Laboratories report to Metal Finisher's
Foundation, July 6, 1973.
(13) Dodge, B. F., and zabban, W., "Disposal of Plating Room
Wastes. III. Cyanide Wastes; Treatment With Hypochlo-
rites and Removal of Cyanates", Plating, 3J (6), 561-586
(June 1951) .
Dodge, B. F,, and Zabban, W., "Disposal of Plating Room
199
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Wastes. III. Cyanide Wastes: Treatment with Hypochlo-
rites and Removal of Cyanates. Addendum", Plating, ,39
(4), 385 (April 1952} .
(15) Dodge, B. F. , and Zabban, W., "Disposal of Plating Room
Wastes. IV. Batch Volatilization of Hydrogen Cyanide
From Aqueous Solutions of Cyanides", Plating, 3,9 (10) ,
1133-1139 (October 1952).
(16) Dodge, B. F., and Zabban, W., "Disposal of Plating Room
Wastes. IV. Batch Volatilization of Hydrogen Cyanide
From Aqueous Solutions of Cyanides. Continuation",
Plating, 39 (11), 1235-1244 (November 1952).
(17 overflow", chemical Week, 111 (24), 47 (December 13,
1972).
(18) Oyler, R. W. , "Disposal of Waste Cyanides by Electro-
lytic Oxidation", Plating, .36 (4), 341-342 (April 1949).
(19) Kurz, H., and Weber, W,, "Electrolytic Cyanide Detoxi-
cation by the CYNOX Process", Galvanotechnik and
Oberflaechenschutz, 3, 92-97 (1962).
(20) "Electrolysis Speeds Up Waste Treatment", Environmental
Science and Technology", 4 (3) , 201 (March 1970) .
(21) Thiele, H., "Detoxification of Cyanide-Containing Waste
Water by Catalytic Oxidation and Adsorption Process",
Fortschritte Wasserchemie Ihrer Grenzgebiete, 9, 109-
120 (1968): CA, 70* *»054 (1969).
(22) Bucksteeg, W., "Decomposition of Cyanide Wastes by
Methods of Catalytic Oxidation Absorption", Proceedings
of the 21st Industrial waste conference, Purdue Univer-
sity Engineering Extension series, 688-695 (1966).
(23) "Destroy Free Cyanide in Compact, Continuous Unit11,
Calgon Corporation advertisement. Finishers1 Management,
18 (2), 14 (February 1973).
(24) Sondak, N. S., and Dodge, B. F., "The Oxidation of
Cyanide Bearing Plating Wastes by Ozone, part I",
Plating, 48 (2), 173-180 (February 1961) .
(25) sonday, N. E., and Dodge, B. F., "The Oxidation of
Cyanide Bearing Plating Wastes by Ozone. Part ii".
Plating, 48 (3), 280-284 (March 1961).
(26) Rice, Rip G. , letter from Effluent Discharge Effects
Committee to Mr. Allen Cywin, Effluent Guidelines
Division, July 9, 1973.
(27) "Cyanide Wastes Might Be Destroyed at One-Tenth the
Conventional Cost", Chemical Engineering, 79 (29), 20
200
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(December 25, 1972) .
(28) Manufacturers1 Literature, BMP Corporation, Charlotte,
North Carolina (1973) .
(29) Ible, N., and Frei, A. M., "Electrolytic Reduction of
Chrome in Waste Water", Galvanotechnik und Qberflaech-
ensehutz, 5 (6), 117-122 (1964).
(30) Schulze, G., "Electrochemical Reduction of Chromic
Acid-Containing Waste Water", Galvanotechnik, 56 (7) ,
475-480 (1967) : CA, 6J, 15876t (1968) .
(31) Anderson, J. R., and Weiss, Charles O., "Method for
Precipitation of Heavy Metal sulfides", U. S. Patent
No. 3,740,331, June 19, 1973.
(32) Lancy, L. E., and Rice, R. L., "Upgrading Metal Finish-
ing Facilities to Reduce Pollution", paper presented at
the EPA Technology Transfer Seminar, New York, N.Y.
(December 1972).
(33) Electroplating Engineering Handbook, Edited by A. K.
Graham, Third Edition, Van Nostrand Reinhold Company,
New York (1971).
(34) Olsen, A. E., "Upgrading Metal Finishing Facilities to
Reduce Polluticn; In-Process Pollution Abatement
Practices", paper presented at the EPA Technology
Transfer Seminar, New York, N. Y. (December, 1972) .
(35) Novotny, C. J,, "Water Use and Recovery", Finishers*
Management, 18 (2), 43-46 +50 (February 1973).
(36) Rushmere, J. D., "Process for Brightening Zinc and
Cadmium Electroplates Using an Inner Salt of a Quaternary
Pyridine Carboxylic Acid and Composition Containing the
Same", U. S. Patent 3,411,996, November 19, 1968.
(37) Ceresa, M., and Lancy, L. E., "Metal Finishing Waste
Disposal. Part Two", Metal Finishing, 66, (5) , 60-65
(May 1968).
(38) Ceresa, M., and Lancy, L. E., "Metal Finishing Waste
Disposal. Part Three", Metal Finishing, 66, (6), 112-
118" (June 1968) .
(40) Brown, C. J., et al., "Plating Waste Recovery by
Reciprocating-Flow Ion Exchange11, Technical Conference
of The American Electroplaters" Society, Minneapolis,
Minnesota, June 18, 1973.
(41) Oh, C. B., and Hartley, H. S., "Recycling Plating Wastes
by Vapor Recompression", Products Finishing, 36 (8),
90-96 (May 1972) .
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(42) Kolesat, T. J. , "Employment of Atmospheric Evaporative
Towers in the Electroplating Industry as a Means of
Recycle and Waste Elimination", Technical conference
of The American Electroplaters' Society, Minneapolis,
Minnesota, June 18, 1973.
(43) McLay, W. J., Corning Glass Company, Personal Communi-
cation.
(44) Spatz, D. D., "Industrial Waste Processing With Reverse
Osmosis", Osmonics, Inc., Hopkins, Minnesota (August 1,
1971) .
(45) Spatz, D. D., "Electroplating Waste Water Processing
With Reverse osmosis", Products Finishing, J.6 (11) ,
79-89 (August 1972) .
(46) Campbell, R. J., and Emmerman, D. K., "Recycling of
Water From Metal Finishing Wastes by Freezing Processes",
ASME Paper 72-PID-7 (March 1972),
(47) Campbell, R. J., and Immerman, D. K., "Freezing and
Recycling of Plating Rinsewater", Industrial Water
Engineering, J (4), 38-39 (June/July 1972).
(48) Tcbcuwiner, Sidney B., "investigation of Treating
Electroplaters Cyanide Waste by Electrodialysis,"
EPA A-R2-73-287 December, 1973.
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SECTION XIV
GLOSSARY
An acidic solution for activating the workpiece surface prior to
electroplating in an acidic solution, especially after the
workplace has been processed in an alkaline solution.
Acidity
The concentration of acid ions expressed as pH for a solution.
Act
The Federal Water Pollution Control Act Amendments of 1972.
Activator
Chemical substance, usually stannous chloride, that triggers the
electroless deposition process on a nonconducting surface.
Addi + ion __ Agent
Substance, usually an organic material, added to an electro-
plating solution to improve the properties of the electroplate.
The concentration of base ions expressed as pH for a solution.
Allowable Water Use
The sum of water used for each plating process or the sum of
water used for each necessary rinsing operation.
Amgere
Unit of electricity, amount of which is the current that will
deposit silver at the rate of 0.0011180 gram per second.
Ampere- hours
Product of amperes of electricity being used and time of that
use.
Anions
The negative charge ions in the solution, i.e., hydroxyl.
Anode
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The electrode that takes electrons from the anions in solution
(is connected to the positive terminal of the direct current
source) .
Automatic^ Plat ing
(1) full - plating in which the cathodes are automatically
conveyed through successive cleaning and plating tanks.
(2) semi - plating in which the cathodes are conveyed auto-
matically through cnly one plating tank.
BarrelJPlating
Electroplating of workpieces in barrels (bulk) .
Basis^Metal or Mater ial
That substance of which the workpieces are made and that receives
the electroplate and the treatments in preparation for plating.
Best ^ Aya il able Tec hno logy EgonQinicaj.!^ Achievable
Level of technology applicable to effluent limitations to be
achieved by July I, 1983, for industrial discharges to surface
waters as defined by Section 301 (b) (2) (A) of the Act.
Best Practicable Control Teghnology Currently Available
Level of technology applicable to effluent limitations to be
achieved by July 1, 1977, for industrial discharges to surface
waters as defined by Section 301 (b) (1) (A) of the act.
BOD
Biochemical oxygen demand.
A solution used to produce a bright surface on a metal.
Capital_Costs
Financial charges which are computed as the cost of capital times
the capital expenditures for pollution control. The cost of
capital is based upon a weighed average of the separate costs of
debt and equity.
Captive Operation
Electroplating facility owned and operated by the same organi-
zation that manufactures the workpieces.
Captive Plating Shops
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Companies engaged in product fabrication and/or assembly and
normally process approximately -the same number of the same
products per month. The volume of toxic wastes created by
captive operations is expected to be more or less constant.
Car.bqn_Bed Catalytic..__De:strpction
A nonelectrolytic process for the catalytic oxidation of cyanide
wastes using trickling filters filled with low-temperature coke.
chemical substance, usually palladium chloride, in a dip solution
to cause electro less deposition of a metal on a nonconducting
surface.
Category and Subcategory
Divisions of a particular industry which possess different traits
which affect waste treatability and would require different
effluent limitations.
Cathode
The electrode (the workpieces in electroplating) that transfers
electrons to the cations in the solution.
Cations
The positive- charge ions in the solution, i.e., the metal to be
electrodeposited, hydrogen, copper, nickel, etc,
Chelate compound
A compound in which the metal is contained as an integral part of
a ring structure and is not readily ionized.
A compound capable of forming a chelate compound with a metal
ion.
Chemical Recover y Systems
Chemical treatment of electroplating wastes utilizing (1) batch
methods, (2) continuous methods, or <3) integrated procedures.
Chroini.um_Catal^st
Plating bath constituent that in small amounts makes possible the
continuing capability to electrodeposit chromium. Usually
fluoride, fluorosilicate and/or sulfate.
Cleaner
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Usually an alkaline solution pretreatment to remove surface soil
such as oils, greases, and substrates chemically unrelated to the
basis material.
A system used for the recovery of chemicals and water from a
plating line. An evaporator concentrates flow from the rinse
water holding tank. The concentrated rinse solution is returned
to the plating bath, and distilled water is returned to the final
rinse tank. The system is designed for recovering 100 percent of
the chemicals, normally lost in dragout, for reuse in the plating
process.
COD
Chemical oxygen demand.
Compatible Pollutants
Those pollutants which can be adequately treated in publicly
owned treatment works without harm to such works.
Continuous_Treatment
Chemical waste treatment operating uninterruptedly as opposed to
batch treatment; sometimes referred to as flow through treatment.
C gnyer si on ^Coat ing
A coating produced by chemical or electrochemical treatment of a
metallic surface that gives a superficial layer containing a
compound of the metal, for example, chromate coatings on zinc and
cadmium, oxide coatings on steel.
Coulomb
Product of current in amperes and time in seconds. Thus, one
coulomb is 1 ampere-second.
Coulombic
A. term used to denote a relationship based in coulombs and
electrochemical equivalents according to Faraday's Law,
Counterf low_ Rinsing
Series of rinses; usually three, in which water flow is from last
to first rinse, thus counterflow to direction work loads move
through the rinses.
d-c Power Source
Direct Current power source,
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Refers -to the multilayer electroplate of copper * nickel +
chromium in that order, on the basis material to provide the
bright decorative appearance.
Deposit
The material formed on the electrode or workpiece surface, i.e.,
a metal in electroplating.
De pr eciat i on
Accounting charges reflecting the deterioration of a capital
asset over its useful life.
Dragout
The solution that adheres to the objects removed from a bath.
More precisely defined as that solution which is carried past the
edge of the tank.
Dual _ Mcke 1_ PI a t e
Two layers of nickel electroplate with different properties to
enhance corrosion resistance and appearance under chromium
electroplate. Requires two different nickel plating baths.
Effluent
The waste water discharged from a point source to navigable
waters.
A maximum amount per unit of production of each specific
constituent of the effluent that is subject to limitation in the
discharge from a point source.
Electrochernical_Equivalent
The weight of metal electrodeposited (or other substance changed
chemically by reduction or oxidation) per unit of time and unit
of current; i.e., pound per ampere-hour, grams per ampere-second.
Electrode
Conducting material for passing the electric current out of a
solution by taking up or into it by giving up electrons from or
to ions in the solution.
The transfer of electrons from the cathode -to metal ions at its
surface to produce the metal on the cathode surface.
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E^ectreforming
The production or reproduction of articles by electrodeposition
upon a mandrel or mold that is subsequently separated from the
deposit.
Electroless Plating
Deposition of a metallic coating by a controlled chemical
reduction that is catalyzed by the metal or alloy being
deposited.
Elect ro J. y_s is
The passage of current through an electrolyte bringing about
chemical reactions.
ElectrolyticCell
A unit apparatus in which electrochemical reactions are produced
by applying electrical energy, or which supplies electrical
energy as a result of chemical reactions and which includes two
or more electrodes and one or more electrolytes contained in a
suitable vessel.
Electro j.^tic^Decomposit ion
An electrochemical treatment used for the oxidation of cyanides.
The method is practical and economical when applied to
concentrated solutions such as contaminated baths, cyanide dips,
stripping solutions, and concentrated rinses. Electrolysis is
carried out at a current density of 35 amp/sq ft at the anode and
70 amp/sq ft at the cathode. Metal is deposited at the cathode
and can be reclaimed.
Electroplating
The electrodeposition of an adherent metallic coating upon the
basis metal or material for the purpose of securing a surface
with properties or dimensions different from those of the basis
metal or material.
Electroplating^ JPrgce ss
An electroplating process includes a succession of operations
starting with cleaning in alkaline solutions, acid dipping to
neutralize or acidify the wet surface of the parts, followed by
electroplating, rinsing to remove the processing solution from
the workplaces, and drying.
Exhaust Wash
Water used to trap droplets and solubles from air passed to
remove spray, vapor, and gasses from electroplating and process
tanks.
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The number of coulombs (96,490) required for an electrochemical
reaction involving one chemical equivalent.
(1) true - the actual concentration of cyanide radical, or
equivalent alkali cyanide, not combined in complex ions with
metals in solutions.
(2) calculated - the concentration of cyanide, or alkali
cyanide, present in solution in excess of that calculated as
necessary to form a specified complex ion with a metal or metals
present in solution.
(3) analytical - the free cyanide content of a solution as
determined by a specified analytical method.
Hard_Chrome
Chromium electroplate applied for nondecorative use such as wear
resistance in engineering applications.
A metallic deposit produced by a displacement reaction in which
one metal displaces another from solution, for example:
Fe + Cu++ T Cu * Fe+4-
Those pollutants which would cause harm to, adversely affect the
performance of, or be inadequately treated in publicly owned
treatment works.
I n degenden tjQ|ge r a t. io n
Job shop or contract shop in which electroplating is done on
workpieces owned by the customer.
A, waste treatment method in which a chemical rinse tank is
inserted in the plating line between the process tank and the
water rinse tank. The chemical rinse solution is continuously
circulated through the tank and removes the dragout while
reacting chemicals with it.
The capital expenditures required to bring the treatment or
control technology into operation. These include the traditional
expenditures such as design; purchase of land and materials;
209
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etc.; plus any additional expenses required to bring the
technology into operation including expenditures to establish
related necessary solid waste disposal.
Joint Treatment
Treatment in publicly owned treatment works of combined municipal
wastewaters of domestic origin and wastewaters from other
sources.
Mandrel
A form used as a cathode in electroforming; a mold or matrix.
New__Source
Any building, structure, facility, or installation from which
there is or may be a discharge of pollutants and whose
construction is commenced after the publication of the proposed
regulations.
New^Source:Performance Standards
Performance standards for the industry and applicable new sources
as defined by Section 306 of the Act.
ohm
The unit of electrical resistance. The resistance at OC of a
column of mercury of uniform cross section, having a length of
106.300 cm and a mass of 14.4521 gm.
Open-Loop Evaporation System
A system used for the partial recovery of chemicals and water
from a plating line using less than 3 rinses. The circulation
loop through the evaporator is opened by creating another flow
path resulting in wastewater. A small percentage {4-5 percent)
of the dragout that accumulates in the final rinse is not
recirculated to the evaporator and must be treated by a chemical
method before disposal.
ORPiiiu Recorder s
Oxidation-reduction potential recorders.
Oxidizable^gyanide
Cyanide amenable to oxidation by chlorine according to standard
analytical methods.
21
A unit for measuring acidity or alkalinity of water, based on
hydrogen ion concentrations. A pH of 7 indicates a "neutral"
210
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water or solution. At pH lower than 7, a solution is acidic. At
pH higher than 7, a solution is alkaline.
PjLekle
An acid solution used to remove oxides or other compounds related
to the basis metal from its surface of a metal by chemical or
electrochemical action.
The removal .of oxides or other compounds related to the basis
metal from its surface by immersion in a pickle.
Elated Area
The area of the workpiece receiving an electrodeposit. The
thickness of deposit usually varies over the plated area,
plating Barrel
Container in which parts are placed loosely, so they can tumble
as the barrel rotates in the plating or processing solution.
Elating Ragjj
Fixture that permits moving one or more workpieces in and out of
a treating or plating tank and transferring electric current to
the workpieces when in the -tank.
A single source of water discharge such as an individual plant.
Pregla.ti.ng^Treatment_Waste
Waste contributed by preplating treatments is affected by the
basis materials, any surface soil on the workpieces, formulation
of solutions used for cleaning or activating the materials, solu-
tion temperatures, and cycling times,
gretreatment
Treatment performed in wastewaters from any source prior to
introduction for joint treatment in publicly owned treatment
works.
Rack ^Plating
Electroplating of workpieces on racks,
Reclaim^ Rinses
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Reclaim rinses are used as the first step following a plating
process to retain as much of the chemicals as possible and to
allow return of the dragout solution to the plating tank.
Rectifier
A device which converts ac into dc by virtue of a characteristic
permitting appreciable flow of current in only one direction,
Reverse osmogis
h recovery process in which the more concentrated solution is put
under a pressure greater than the osmotic pressure to drive water
across the membrane to the dilute stream while leaving behind the
dissolved, salts.
ginse
Water for removal of dragout by dipping, spraying, fogging, etc.
Rochelle ...Sa^t
Sodium potassium tart rate: KNaC
-------
Term for vessel that contains the solution and auxiliary equip-
ment for carrying out the electroplating or other operational
step.
Tank current
Total amperage required to electroplate all the workpieces of a
tank load.
Tank^Load
Total number of workpieces being processed simultaneously in the
tank.
Total^Chromium
Total chromium (CrT) is the sum of chromium in all valences.
Tot al Cy anide
The total content of cyanide expressed as the radical CN-, or
alkali cyanide whether present as simple or complex ions. The
sum of both the combined and free cyanide content of a plating
solution. In analytical terminology, total cyanide is the sum of
cyanide amenable to oxidation by chlorine and that which is not
according to standard analytical methods.
Total_Meta,l
Total metal is the sum of the metal content in both soluble and
insoluble form.
Unit:.T Operation
A single, discrete process as part of an overall sequence, e.g.,
precipitation, settling, filtration.
Used_Current
Current that is used in electroplating operations and related to
{!) the area being pla##d for a particular deposit thickness and
(2) the processing time (area per unit time) .
Volt
The voltage which will produce a current of one ampere through a
resistance of one ohm.
watt
An energy rate of one joule per second, or the power of an
electric current of one ampere with an intensity of one volt.
Wo.rk.BJ eg e
The item to be electroplated.
213
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TABLE 36
METRIC UNITS
CONVERSION TABLE
KTJtTIPLY (ENGLISH UNITS)
ENGLISH UNIT ABBREVIATION
acre ac
acre - feet ac ft
British Thermal
Unit BTU
British Thermal BTU/lb
Unit/pound
cubic feet/minute cfffi
cubic feet/second cfs
cubic feet cu Tt
cubic feet cu ft
cubic inches cu in
degree Fahrenheit °F
feet ft
gallon gal
gallon/minute gpm
horsepower hp
Inches in
inches of mercury in Hg
pounds lb
million gallons/day mgd
mile mi
pound/square inch psig
(gauge)
square feet sq ft
square inches sq in
tons (short) ton
yard yd
by TO OBTAIN; (METRIC UNITS)
CONVERSION ABBREVIATION METRIC UNIT
hectares
cubic meters
0.405
1233.5
0.252
0,555
0.028
1.7
0.028
28.32
16.39
Q.555(°F-32)*
0.3048
3.785
0.0631
0.7457
2.54
0.03342
0.454
3,785
1.609
ha
cu m
kg cal
kg cal/kg
cu m/min
cu m/min
cu m
1
cu cm
"C
m
1
I/sec
kw
cm
a to
kg
cu n/day
km
(0.06805 psig +l)*at«
0,0929
6.452
0.907
0.9144
sq m
sq cm
kkg
m
kilogran-caleries
kilogram calories/
kilogram
cubic tnecers/ninute
cubic meters/minute
cubic meters
liters
cubic centimeters
degree Centigrade
meters
liters
liters/second
killowatts
centimeters
atmospheres
kilograms
cubic meters/day
kilometer
atmospheres
. (absolute)
square meters
square centimeters
metric tons
(1000 kilograms)
meters
Actual conversion, not a multiplier
& GOVERNMENT PRINTING OFFICE:1<>74 54f,-3i8/J45 1-3
214
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ArMiiC DATA 1 • • ^I'l'it N
•:ion No.
4. Title uni.Nuhi isk-
Development Document for Effluent Limitations Guidelines and
Hew Source Performance Standards for the Copper, Hickel,
Chromium, and Zinc Segment of the Electroplating Point Source
'March 1971*
Kit R. Krickenberger
9. Performing Organization NariK ^'.sid Address
Environmental Protection Agency
Effluent Guidelines Division
WSM-E, Em. 913, WH-U52
1p. f 'rojcct/Tiisl: : w url.- Unit No. j
IA
li, Contract/Crane N;;-
68-01-0592
12, Sponsoring Organization, Namr and
Same as #9.
15. Supplementary Notes
Ifi. Abstracts This document presents the findings "of an extensive study of tie
industry by the Environmental Protection Agency for the purpose of developing effluent
limitations guidelines, standards of performance, and pretreatment standards for the
industry to implement Sections 30Mb) and 306 of the "Act."
Effluent limitations guidelines are set forth for the degree of
effluent reduction attainable through the application of the "Best
Practicable Control Technology Currently Available" and the "Best Available
Technology Economically Achievable" which must be achieved by existing
point sources by July 1, 1977 and July 1, 1983, respectively. The "Standards
of Performance for Hew Sources" set forth a degree of effluent reduction
which is achievable through the application of the best available demonstrated
control technology processes, operating methods or other alternatives.
17. Key Words and Document Analysis. I7c. Descriptors
17b. Identifiers/Open-Ended Terms
17c. COSATl Fit-Id-'Group
19.. Security "Class (Tbii |21. No. of Pages
Report)
18. Availability Statement
GPO, Washington, DC
«• -. v>;^4f ^ ..I..—
20. Security Class {Tbi.s
u .„,.
J
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